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Hansen CE, Springstubbe D, Müller S, Petkovic S. Directed Circularization of a Short RNA. Methods Mol Biol 2024; 2765:209-226. [PMID: 38381342 DOI: 10.1007/978-1-0716-3678-7_12] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/22/2024]
Abstract
Basic research and functional analyses of circular RNA (circRNA) have been limited by challenges in circRNA formation of desired length and sequence in adequate yields. Nowadays, circular RNA can be obtained using enzymatic, "ribozymatic," or modulated splice events. However, there are few records for the directed circularization of RNA. Here, we present a proof of principle for an affordable and efficient RNA-based system for the controlled synthesis of circRNA with a physiological 3',5'-phosphodiester conjunction. The engineered hairpin ribozyme variant circular ribozyme 3 (CRZ-3) performs self-cleavage poorly. We designed an activator-polyamine complex to complete cleavage as a prerequisite for subsequent circularization. The developed protocol allows synthesizing circRNA without external enzymatic assistance and adds a controllable way of circularization to the existing methods.
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Affiliation(s)
| | | | - Sabine Müller
- University Hospital Schleswig-Holstein, Campus Lübeck, Germany
| | - Sonja Petkovic
- University Hospital Schleswig-Holstein, Campus Lübeck, Germany.
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2
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Jiang W, Long X, Li Z, Hu M, Zhang Y, Lin H, Tang W, Ouyang Y, Jiang L, Chen J, He P, Ouyang X. The Role of Circular RNAs in Ischemic Stroke. Neurochem Res 2023:10.1007/s11064-023-03935-7. [PMID: 37126193 DOI: 10.1007/s11064-023-03935-7] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/25/2022] [Revised: 03/29/2023] [Accepted: 03/31/2023] [Indexed: 05/02/2023]
Abstract
Ischemic stroke (IS), a devastating condition characterized by intracranial artery stenosis and middle cerebral artery occlusion leading to insufficient oxygen supply to the brain, is a major cause of death and physical disability worldwide. Recent research has demonstrated the critical role of circular RNAs (circRNAs), a class of covalently enclosed noncoding RNAs that are widespread in eukaryotic cells, in regulating various physiological and pathophysiological cellular processes, including cell apoptosis, autophagy, synaptic plasticity, and neuroinflammation. In the past few years, circRNAs have attracted extensive attention in the field of IS research. This review summarizes the current understanding of the mechanisms underlying the involvement of circRNAs in IS development. A better understanding of circRNA-mediated pathogenic mechanisms in IS may pave the way for translating circRNA research into clinical practice, ultimately improving the clinical outcomes of IS patients.
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Affiliation(s)
- Weiwei Jiang
- Department of Organ Transplantation, Zhujiang Hospital, Southern Medical University, Guangzhou, Guangdong, China
| | - Xiongquan Long
- Department of Gastroenterology, The First Affiliated Hospital of Hunan Normal University, Hunan Normal University, Changsha, Hunan, China
| | - Zhicheng Li
- Collage of Pharmacy, University of South China, Hengyang, Hunan, China
| | - Mi Hu
- Department of Physiology, Institute of Neuroscience Research, Hengyang Key Laboratory of Neurodegeneration and Cognitive Impairment, University of South China, Hengyang, Hunan, China
| | - Yangkai Zhang
- Department of Physiology, Institute of Neuroscience Research, Hengyang Key Laboratory of Neurodegeneration and Cognitive Impairment, University of South China, Hengyang, Hunan, China
| | - Huiling Lin
- Department of Physiology, Institute of Neuroscience Research, Hengyang Key Laboratory of Neurodegeneration and Cognitive Impairment, University of South China, Hengyang, Hunan, China
| | - Wanying Tang
- Department of Physiology, Institute of Neuroscience Research, Hengyang Key Laboratory of Neurodegeneration and Cognitive Impairment, University of South China, Hengyang, Hunan, China
| | - Yuxin Ouyang
- Department of Physiology, Institute of Neuroscience Research, Hengyang Key Laboratory of Neurodegeneration and Cognitive Impairment, University of South China, Hengyang, Hunan, China
| | - Liping Jiang
- Department of Clinical Pharmacology, Xiangya Hospital, Central South University, Changsha, China
| | - Jinzhi Chen
- Department of Physiology, Institute of Neuroscience Research, Hengyang Key Laboratory of Neurodegeneration and Cognitive Impairment, University of South China, Hengyang, Hunan, China
| | - Pingping He
- The Research Center of Reproduction and Translational Medicine of Hunan Province, Department of Physiology, Medical College, Hunan Normal University, Changsha, 410081, Hunan Province, China
| | - Xinping Ouyang
- Department of Physiology, Institute of Neuroscience Research, Hengyang Key Laboratory of Neurodegeneration and Cognitive Impairment, University of South China, Hengyang, Hunan, China.
- The Research Center of Reproduction and Translational Medicine of Hunan Province, Department of Physiology, Medical College, Hunan Normal University, Changsha, 410081, Hunan Province, China.
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3
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Sun K, Yao H, Zhang P, Sun Y, Ma J, Xia Q. Emerging landscape of circFNDC3B and its role in human malignancies. Front Oncol 2023; 13:1097956. [PMID: 36793611 PMCID: PMC9924128 DOI: 10.3389/fonc.2023.1097956] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/14/2022] [Accepted: 01/06/2023] [Indexed: 01/31/2023] Open
Abstract
In recent years, more attention has been paid to expanding the abundance of Circular RNAs (circRNAs), while the circRNAs that have been found to have significant functions have not been studied in different diseases. CircFNDC3B is one of the most researched circRNAs generated from fibronectin type III domain-containing protein 3B (FNDC3B) gene. Accumulating researches have reported the multiple functions of circFNDC3B in different cancer types and other non-neoplastic diseases, and predicted that circFNDC3B might be a potential biomarker. Notably, circFNDC3B can play roles in different diseases by binding to various microRNAs (miRNAs), binding to RNA-binding proteins (RBPs), or encoding functional peptides. This paper systematically summarizes the biogenesis and function of circRNAs, reviews and discusses the roles and molecular mechanisms of circFNDC3B and its target genes in different cancers and non-neoplastic diseases, which will do favor to broaden our comprehension of the function of circRNAs and facilitate subsequent research on circFNDC3B.
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Affiliation(s)
- Kai Sun
- Department of Urology, Shandong Province Hospital, Shandong University, Jinan, China
| | - Huibao Yao
- Department of Urology, The Affiliated Yantai Yuhuangding Hospital of Qingdao University, Yantai, Shandong, China
| | - Peizhi Zhang
- Department of Urology, Shandong Province Hospital, Shandong University, Jinan, China
| | - Yanning Sun
- Department of Urology, Shandong Province Hospital, Shandong University, Jinan, China
| | - Jian Ma
- Department of Urology, The Affiliated Yantai Yuhuangding Hospital of Qingdao University, Yantai, Shandong, China
| | - Qinghua Xia
- Department of Urology, Shandong Province Hospital, Shandong University, Jinan, China
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4
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Abstract
Covalently closed, single-stranded circular RNAs can be produced from viral RNA genomes as well as from the processing of cellular housekeeping noncoding RNAs and precursor messenger RNAs. Recent transcriptomic studies have surprisingly uncovered that many protein-coding genes can be subjected to backsplicing, leading to widespread expression of a specific type of circular RNAs (circRNAs) in eukaryotic cells. Here, we discuss experimental strategies used to discover and characterize diverse circRNAs at both the genome and individual gene scales. We further highlight the current understanding of how circRNAs are generated and how the mature transcripts function. Some circRNAs act as noncoding RNAs to impact gene regulation by serving as decoys or competitors for microRNAs and proteins. Others form extensive networks of ribonucleoprotein complexes or encode functional peptides that are translated in response to certain cellular stresses. Overall, circRNAs have emerged as an important class of RNAmolecules in gene expression regulation that impact many physiological processes, including early development, immune responses, neurogenesis, and tumorigenesis.
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Affiliation(s)
- Li Yang
- Center for Molecular Medicine, Children's Hospital, Fudan University and Shanghai Key Laboratory of Medical Epigenetics, International Laboratory of Medical Epigenetics and Metabolism, Ministry of Science and Technology, Institutes of Biomedical Sciences, Fudan University, Shanghai, China;
| | - Jeremy E Wilusz
- Verna and Marrs McLean Department of Biochemistry and Molecular Biology, Therapeutic Innovation Center, Baylor College of Medicine, Houston, Texas, USA;
| | - Ling-Ling Chen
- State Key Laboratory of Molecular Biology, Shanghai Key Laboratory of Molecular Andrology, CAS Center for Excellence in Molecular Cell Science, Shanghai Institute of Biochemistry and Cell Biology, University of Chinese Academy of Sciences, Chinese Academy of Sciences, Shanghai, China;
- School of Life Science and Technology, ShanghaiTech University, Shanghai, China
- School of Life Science, Hangzhou Institute for Advanced Study, University of Chinese Academy of Sciences, Hangzhou, China
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5
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The emerging role of circular RNAs in cardiovascular diseases. J Physiol Biochem 2021; 77:343-353. [PMID: 33772724 DOI: 10.1007/s13105-021-00807-y] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/14/2020] [Accepted: 03/03/2021] [Indexed: 12/23/2022]
Abstract
Cardiovascular disease (CVD) is one of the vital causes of morbidity and mortality, and the number of deaths from CVD has increased worldwide. Circular RNAs (circRNAs) is a novel type of endogenous noncoding RNA, which can form covalent closed continuous rings and are highly expressed in the eukaryotic transcriptome. In recent years, research on circRNAs have been increasing and the researchers have also become cumulatively aware of the association between circRNAs and CVD. This review highlights the biogenesis and functions of circRNAs and the role in cardiovascular diseases.
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6
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LaRoche-Johnston F, Monat C, Verreault E, Cousineau B. Molecular characterization of both transesterification reactions of the group II intron circularization pathway. Nucleic Acids Res 2021; 49:6996-7010. [PMID: 34157113 PMCID: PMC8266578 DOI: 10.1093/nar/gkab537] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/25/2020] [Revised: 06/05/2021] [Accepted: 06/10/2021] [Indexed: 11/30/2022] Open
Abstract
Group II introns can self-splice from RNA transcripts through branching, hydrolysis and circularization, being released as lariats, linear introns and circles, respectively. In contrast to branching, the circularization pathway is mostly based on assumptions and has been largely overlooked. Here, we address the molecular details of both transesterification reactions of the group II intron circularization pathway in vivo. We show that free E1 is recruited by the intron through base pairing interactions and that released intron circles can generate free E1 by the spliced exon reopening reaction. The first transesterification reaction was found to be induced inaccurately by the 3′OH of the terminal residue of free E1 at the 3′ splice site, producing circularization intermediates with heterogeneous 3′ ends. Nevertheless, specific terminal 3′OH, selected by a molecular ruler, was shown to precisely attack the 5′ splice site and release intron circles with 3′–5′ rather than 2′–5′ bonds at their circularization junction. Our work supports a circularization model where the recruitment of free E1 and/or displacement of cis-E1 induce a conformational change of the intron active site from the pre-5′ to the pre-3′ splice site processing conformation, suggesting how circularization might initiate at the 3′ instead of the 5′ splice site.
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Affiliation(s)
- Félix LaRoche-Johnston
- Department of Microbiology and Immunology, McGill University, Montréal, QC H3A 2B4, Canada
| | - Caroline Monat
- Department of Microbiology and Immunology, McGill University, Montréal, QC H3A 2B4, Canada
| | - Erika Verreault
- Department of Microbiology and Immunology, McGill University, Montréal, QC H3A 2B4, Canada
| | - Benoit Cousineau
- Department of Microbiology and Immunology, McGill University, Montréal, QC H3A 2B4, Canada
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7
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A Singular and Widespread Group of Mobile Genetic Elements: RNA Circles with Autocatalytic Ribozymes. Cells 2020; 9:cells9122555. [PMID: 33260527 PMCID: PMC7761336 DOI: 10.3390/cells9122555] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/23/2020] [Revised: 11/19/2020] [Accepted: 11/26/2020] [Indexed: 11/16/2022] Open
Abstract
Circular DNAs, such as most prokaryotic and phage genomes, are a frequent form of nucleic acids, whereas circular RNAs had been regarded as unusual macromolecules until very recently. The first reported RNA circles were the family of small infectious genomes of viroids and circular RNA (circRNA) satellites of plant viruses, some of which contain small self-cleaving RNA motifs, such as the hammerhead (HHR) and hairpin ribozymes. A similar infectious circRNA, the unique human hepatitis delta virus (HDV), is another viral satellite that also encodes self-cleaving motifs called HDV ribozymes. Very recently, different animals have been reported to contain HDV-like circRNAs with typical HDV ribozymes, but also conserved HHR motifs, as we describe here. On the other hand, eukaryotic and prokaryotic genomes encode sequences able to self-excise as circRNAs, like the autocatalytic Group I and II introns, which are widespread genomic mobile elements. In the 1990s, the first circRNAs encoded in a mammalian genome were anecdotally reported, but their abundance and importance have not been unveiled until recently. These gene-encoded circRNAs are produced by events of alternative splicing in a process generally known as backsplicing. However, we have found a second natural pathway of circRNA expression conserved in numerous plant and animal genomes, which efficiently promotes the accumulation of small non-coding RNA circles through the participation of HHRs. Most of these genome-encoded circRNAs with HHRs are the transposition intermediates of a novel family of non-autonomous retrotransposons called retrozymes, with intriguing potential as new forms of gene regulation.
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8
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Molina-Sánchez MD, Toro N. DNA cleavage and reverse splicing of ribonucleoprotein particles reconstituted in vitro with linear RmInt1 RNA. RNA Biol 2019; 16:930-939. [PMID: 30943851 DOI: 10.1080/15476286.2019.1601379] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022] Open
Abstract
The RmInt1 group II intron is an efficient self-splicing mobile retroelement that catalyzes its own excision as lariat, linear and circular molecules. In vivo, the RmInt1 lariat and the reverse transcriptase (IEP) it encodes form a ribonucleoprotein particle (RNP) that recognizes the DNA target for site-specific full intron insertion via a two-step reverse splicing reaction. RNPs containing linear group II intron RNA are generally thought to be unable to complete the reverse splicing reaction. Here, we show that reconstituted in vitro RNPs containing linear RmInt1 ΔORF RNA can mediate the cleavage of single-stranded DNA substrates in a very precise manner with the attachment of the intron RNA to the 3´exon as the first step of a reverse splicing reaction. Notably, we also observe molecules in which the 5´exon is linked to the RmInt1 RNA, suggesting the completion of the reverse splicing reaction, albeit rather low and inefficiently. That process depends on DNA target recognition and can be successful completed by RmInt1 RNPs with linear RNA displaying 5´ modifications.
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Affiliation(s)
- María Dolores Molina-Sánchez
- a Structure, Dynamics and Function of Rhizobacterial Genomes, Grupo de Ecología Genética de la Rizosfera, Department of Soil Microbiology and Symbiotic Systems , Estación Experimental del Zaidín, Consejo Superior de Investigaciones Científicas , Granada , Spain
| | - Nicolás Toro
- a Structure, Dynamics and Function of Rhizobacterial Genomes, Grupo de Ecología Genética de la Rizosfera, Department of Soil Microbiology and Symbiotic Systems , Estación Experimental del Zaidín, Consejo Superior de Investigaciones Científicas , Granada , Spain
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9
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Molina-Sánchez MD, García-Rodríguez FM, Toro N. Functionality of In vitro Reconstituted Group II Intron RmInt1-Derived Ribonucleoprotein Particles. Front Mol Biosci 2016; 3:58. [PMID: 27730127 PMCID: PMC5037169 DOI: 10.3389/fmolb.2016.00058] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/28/2016] [Accepted: 09/12/2016] [Indexed: 01/22/2023] Open
Abstract
The functional unit of mobile group II introns is a ribonucleoprotein particle (RNP) consisting of the intron-encoded protein (IEP) and the excised intron RNA. The IEP has reverse transcriptase activity but also promotes RNA splicing, and the RNA-protein complex triggers site-specific DNA insertion by reverse splicing, in a process called retrohoming. In vitro reconstituted ribonucleoprotein complexes from the Lactococcus lactis group II intron Ll.LtrB, which produce a double strand break, have recently been studied as a means of developing group II intron-based gene targeting methods for higher organisms. The Sinorhizobium meliloti group II intron RmInt1 is an efficient mobile retroelement, the dispersal of which appears to be linked to transient single-stranded DNA during replication. The RmInt1IEP lacks the endonuclease domain (En) and cannot cut the bottom strand to generate the 3' end to initiate reverse transcription. We used an Escherichia coli expression system to produce soluble and active RmInt1 IEP and reconstituted RNPs with purified components in vitro. The RNPs generated were functional and reverse-spliced into a single-stranded DNA target. This work constitutes the starting point for the use of group II introns lacking DNA endonuclease domain-derived RNPs for highly specific gene targeting methods.
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Affiliation(s)
- Maria D Molina-Sánchez
- Structure, Dynamics and Function of Rhizobacterial Genomes, Department of Soil Microbiology and Symbiotic Systems, Estación Experimental del Zaidín, Consejo Superior de Investigaciones Científicas Granada, Spain
| | - Fernando M García-Rodríguez
- Structure, Dynamics and Function of Rhizobacterial Genomes, Department of Soil Microbiology and Symbiotic Systems, Estación Experimental del Zaidín, Consejo Superior de Investigaciones Científicas Granada, Spain
| | - Nicolás Toro
- Structure, Dynamics and Function of Rhizobacterial Genomes, Department of Soil Microbiology and Symbiotic Systems, Estación Experimental del Zaidín, Consejo Superior de Investigaciones Científicas Granada, Spain
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10
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Abstract
Circular RNAs (circRNAs) are produced from precursor mRNA (pre-mRNA) back-splicing of thousands of genes in eukaryotes. Although circRNAs are generally expressed at low levels, recent findings have shed new light on their cell type-specific and tissue-specific expression and on the regulation of their biogenesis. Furthermore, the data indicate that circRNAs shape gene expression by titrating microRNAs, regulating transcription and interfering with splicing, thus effectively expanding the diversity and complexity of eukaryotic transcriptomes.
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Affiliation(s)
- Ling-Ling Chen
- State Key Laboratory of Molecular Biology, CAS Center for Excellence in Molecular Cell Science, Institute of Biochemistry and Cell Biology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, 320 Yueyang Road, 200031 Shanghai, China
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11
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Toro N, Molina-Sánchez MD, Nisa-Martínez R, Martínez-Abarca F, García-Rodríguez FM. Bacterial Group II Introns: Identification and Mobility Assay. Methods Mol Biol 2016; 1400:21-32. [PMID: 26895044 DOI: 10.1007/978-1-4939-3372-3_2] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 04/21/2023]
Abstract
Group II introns are large catalytic RNAs and mobile retroelements that encode a reverse transcriptase. Here, we provide methods for their identification in bacterial genomes and further analysis of their splicing and mobility capacities.
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Affiliation(s)
- Nicolás Toro
- Grupo de Ecología Genética de la Rizosfera, Estación Experimental del Zaidín, Consejo Superior de Investigaciones Científicas, Profesor Albareda 1, 18008, Granada, Spain.
| | - María Dolores Molina-Sánchez
- Grupo de Ecología Genética de la Rizosfera, Estación Experimental del Zaidín, Consejo Superior de Investigaciones Científicas, Profesor Albareda 1, 18008, Granada, Spain
| | - Rafael Nisa-Martínez
- Grupo de Ecología Genética de la Rizosfera, Estación Experimental del Zaidín, Consejo Superior de Investigaciones Científicas, Profesor Albareda 1, 18008, Granada, Spain
| | - Francisco Martínez-Abarca
- Grupo de Ecología Genética de la Rizosfera, Estación Experimental del Zaidín, Consejo Superior de Investigaciones Científicas, Profesor Albareda 1, 18008, Granada, Spain
| | - Fernando Manuel García-Rodríguez
- Grupo de Ecología Genética de la Rizosfera, Estación Experimental del Zaidín, Consejo Superior de Investigaciones Científicas, Profesor Albareda 1, 18008, Granada, Spain
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12
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McNeil BA, Semper C, Zimmerly S. Group II introns: versatile ribozymes and retroelements. WILEY INTERDISCIPLINARY REVIEWS-RNA 2016; 7:341-55. [PMID: 26876278 DOI: 10.1002/wrna.1339] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/25/2015] [Revised: 12/10/2015] [Accepted: 12/22/2015] [Indexed: 01/10/2023]
Abstract
Group II introns are catalytic RNAs (ribozymes) and retroelements found in the genomes of bacteria, archaebacteria, and organelles of some eukaryotes. The prototypical retroelement form consists of a structurally conserved RNA and a multidomain reverse transcriptase protein, which interact with each other to mediate splicing and mobility reactions. A wealth of biochemical, cross-linking, and X-ray crystal structure studies have helped to reveal how the two components cooperate to carry out the splicing and mobility reactions. In addition to the standard retroelement form, group II introns have evolved into derivative forms by either losing specific splicing or mobility characteristics, or becoming functionally specialized. Of particular interest are the eukaryotic derivatives-the spliceosome, spliceosomal introns, and non-LTR retroelements-which together make up approximately half of the human genome. On a practical level, the properties of group II introns have been exploited to develop group II intron-based biotechnological tools. WIREs RNA 2016, 7:341-355. doi: 10.1002/wrna.1339 For further resources related to this article, please visit the WIREs website.
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Affiliation(s)
- Bonnie A McNeil
- Department of Biological Sciences, University of Calgary, Calgary, Canada
| | - Cameron Semper
- Department of Biological Sciences, University of Calgary, Calgary, Canada
| | - Steven Zimmerly
- Department of Biological Sciences, University of Calgary, Calgary, Canada
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Monat C, Cousineau B. Circularization pathway of a bacterial group II intron. Nucleic Acids Res 2015; 44:1845-53. [PMID: 26673697 PMCID: PMC4770220 DOI: 10.1093/nar/gkv1381] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/31/2015] [Accepted: 11/26/2015] [Indexed: 12/03/2022] Open
Abstract
Group II introns are large RNA enzymes that can excise as lariats, circles or in a linear form through branching, circularization or hydrolysis, respectively. Branching is by far the main and most studied splicing pathway while circularization was mostly overlooked. We previously showed that removal of the branch point A residue from Ll.LtrB, the group II intron from Lactococcus lactis, exclusively leads to circularization. However, the majority of the released intron circles harbored an additional C residue of unknown origin at the splice junction. Here, we exploited the Ll.LtrB-ΔA mutant to study the circularization pathway of bacterial group II introns in vivo. We demonstrated that the non-encoded C residue, present at the intron circle splice junction, corresponds to the first nt of exon 2. Intron circularization intermediates, harboring the first 2 or 3 nts of exon 2, were found to accumulate showing that branch point removal leads to 3′ splice site misrecognition. Traces of properly ligated exons were also detected functionally confirming that a small proportion of Ll.LtrB-ΔA circularizes accurately. Overall, our data provide the first detailed molecular analysis of the group II intron circularization pathway and suggests that circularization is a conserved splicing pathway in bacteria.
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Affiliation(s)
- Caroline Monat
- Department of Microbiology and Immunology, Microbiome and Disease Tolerance Centre (MDTC), McGill University, Montréal, Québec, Canada H3A 2B4
| | - Benoit Cousineau
- Department of Microbiology and Immunology, Microbiome and Disease Tolerance Centre (MDTC), McGill University, Montréal, Québec, Canada H3A 2B4
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14
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Localization of a bacterial group II intron-encoded protein in human cells. Sci Rep 2015; 5:12716. [PMID: 26244523 PMCID: PMC4525487 DOI: 10.1038/srep12716] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/06/2015] [Accepted: 07/07/2015] [Indexed: 01/06/2023] Open
Abstract
Group II introns are mobile retroelements that self-splice from precursor RNAs to form ribonucleoparticles (RNP), which can invade new specific genomic DNA sites. This specificity can be reprogrammed, for insertion into any desired DNA site, making these introns useful tools for bacterial genetic engineering. However, previous studies have suggested that these elements may function inefficiently in eukaryotes. We investigated the subcellular distribution, in cultured human cells, of the protein encoded by the group II intron RmInt1 (IEP) and several mutants. We created fusions with yellow fluorescent protein (YFP) and with a FLAG epitope. We found that the IEP was localized in the nucleus and nucleolus of the cells. Remarkably, it also accumulated at the periphery of the nuclear matrix. We were also able to identify spliced lariat intron RNA, which co-immunoprecipitated with the IEP, suggesting that functional RmInt1 RNPs can be assembled in cultured human cells.
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15
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Inactivation of group II intron RmInt1 in the Sinorhizobium meliloti genome. Sci Rep 2015; 5:12036. [PMID: 26156864 PMCID: PMC4496777 DOI: 10.1038/srep12036] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/30/2014] [Accepted: 06/15/2015] [Indexed: 11/10/2022] Open
Abstract
Group II introns are self-splicing catalytic RNAs that probably originated in bacteria and act as mobile retroelements. The dispersal and dynamics of group II intron spread within a bacterial genome are thought to follow a selection-driven extinction model. Likewise, various studies on the evolution of group II introns have suggested that they are evolving toward an inactive form by fragmentation, with the loss of the intron 3′-terminus, but with some intron fragments remaining and continuing to evolve in the genome. RmInt1 is a mobile group II intron that is widespread in natural populations of Sinorhizobium meliloti, but some strains of this species have no RmInt1 introns. We studied the splicing ability and mobility of the three full-length RmInt1 copies harbored by S. meliloti 1021, and obtained evidence suggesting that specific mutations may lead to the impairment of intron splicing and retrohoming. Our data suggest that the RmInt1 copies in this strain are undergoing a process of inactivation.
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Monat C, Quiroga C, Laroche-Johnston F, Cousineau B. The Ll.LtrB intron from Lactococcus lactis excises as circles in vivo: insights into the group II intron circularization pathway. RNA (NEW YORK, N.Y.) 2015; 21:1286-1293. [PMID: 25956521 PMCID: PMC4478347 DOI: 10.1261/rna.046367.114] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 02/19/2015] [Accepted: 03/31/2015] [Indexed: 06/04/2023]
Abstract
Group II introns are large ribozymes that require the assistance of intron-encoded or free-standing maturases to splice from their pre-mRNAs in vivo. They mainly splice through the classical branching pathway, being released as RNA lariats. However, group II introns can also splice through secondary pathways like hydrolysis and circularization leading to the release of linear and circular introns, respectively. Here, we assessed in vivo splicing of various constructs of the Ll.LtrB group II intron from the Gram-positive bacterium Lactococcus lactis. The study of excised intron junctions revealed, in addition to branched intron lariats, the presence of perfect end-to-end intron circles and alternatively circularized introns. Removal of the branch point A residue prevented Ll.LtrB excision through the branching pathway but did not hinder intron circle formation. Complete intron RNA circles were found associated with the intron-encoded protein LtrA forming nevertheless inactive RNPs. Traces of double-stranded head-to-tail intron DNA junctions were also detected in L. lactis RNA and nucleic acid extracts. Some intron circles and alternatively circularized introns harbored variable number of non-encoded nucleotides at their splice junction. The presence of mRNA fragments at the splice junction of some intron RNA circles provides insights into the group II intron circularization pathway in bacteria.
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Affiliation(s)
- Caroline Monat
- Department of Microbiology and Immunology, Microbiome and Disease Tolerance Centre (MDTC), McGill University, Montréal, Québec, Canada H3A 2B4
| | - Cecilia Quiroga
- Department of Microbiology and Immunology, Microbiome and Disease Tolerance Centre (MDTC), McGill University, Montréal, Québec, Canada H3A 2B4
| | - Felix Laroche-Johnston
- Department of Microbiology and Immunology, Microbiome and Disease Tolerance Centre (MDTC), McGill University, Montréal, Québec, Canada H3A 2B4
| | - Benoit Cousineau
- Department of Microbiology and Immunology, Microbiome and Disease Tolerance Centre (MDTC), McGill University, Montréal, Québec, Canada H3A 2B4
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17
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Petkovic S, Müller S. RNA circularization strategies in vivo and in vitro. Nucleic Acids Res 2015; 43:2454-65. [PMID: 25662225 PMCID: PMC4344496 DOI: 10.1093/nar/gkv045] [Citation(s) in RCA: 226] [Impact Index Per Article: 25.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/26/2014] [Revised: 01/07/2015] [Accepted: 01/12/2015] [Indexed: 12/30/2022] Open
Abstract
In the plenitude of naturally occurring RNAs, circular RNAs (circRNAs) and their biological role were underestimated for years. However, circRNAs are ubiquitous in all domains of life, including eukaryotes, archaea, bacteria and viruses, where they can fulfill diverse biological functions. Some of those functions, as for example playing a role in the life cycle of viral and viroid genomes or in the maturation of tRNA genes, have been elucidated; other putative functions still remain elusive. Due to the resistance to exonucleases, circRNAs are promising tools for in vivo application as aptamers, trans-cleaving ribozymes or siRNAs. How are circRNAs generated in vivo and what approaches do exist to produce ring-shaped RNAs in vitro? In this review we illustrate the occurrence and mechanisms of RNA circularization in vivo, survey methods for the generation of circRNA in vitro and provide appropriate protocols.
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Affiliation(s)
- Sonja Petkovic
- Institut für Biochemie, Ernst Moritz Arndt Universität Greifswald, Felix-Hausdorff-Str. 4, 17487 Greifswald, Germany
| | - Sabine Müller
- Institut für Biochemie, Ernst Moritz Arndt Universität Greifswald, Felix-Hausdorff-Str. 4, 17487 Greifswald, Germany
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18
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Abstract
It is now clear that there is a diversity of circular RNAs in biological systems. Circular RNAs can be produced by the direct ligation of 5' and 3' ends of linear RNAs, as intermediates in RNA processing reactions, or by "backsplicing," wherein a downstream 5' splice site (splice donor) is joined to an upstream 3' splice site (splice acceptor). Circular RNAs have unique properties including the potential for rolling circle amplification of RNA, the ability to rearrange the order of genomic information, protection from exonucleases, and constraints on RNA folding. Circular RNAs can function as templates for viroid and viral replication, as intermediates in RNA processing reactions, as regulators of transcription in cis, as snoRNAs, and as miRNA sponges. Herein, we review the breadth of circular RNAs, their biogenesis and metabolism, and their known and anticipated functions.
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Affiliation(s)
- Erika Lasda
- Department of Chemistry and Biochemistry, Howard Hughes Medical Institute, University of Colorado, Boulder, Colorado 80309, USA
| | - Roy Parker
- Department of Chemistry and Biochemistry, Howard Hughes Medical Institute, University of Colorado, Boulder, Colorado 80309, USA
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19
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Chillón I, Molina-Sánchez MD, Fedorova O, García-Rodríguez FM, Martínez-Abarca F, Toro N. In vitro characterization of the splicing efficiency and fidelity of the RmInt1 group II intron as a means of controlling the dispersion of its host mobile element. RNA (NEW YORK, N.Y.) 2014; 20:2000-2010. [PMID: 25336586 PMCID: PMC4238363 DOI: 10.1261/rna.047407.114] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 07/21/2014] [Accepted: 09/29/2014] [Indexed: 06/04/2023]
Abstract
Group II introns are catalytic RNAs that are excised from their precursors in a protein-dependent manner in vivo. Certain group II introns can also react in a protein-independent manner under nonphysiological conditions in vitro. The efficiency and fidelity of the splicing reaction is crucial, to guarantee the correct formation and expression of the protein-coding mRNA. RmInt1 is an efficient mobile intron found within the ISRm2011-2 insertion sequence in the symbiotic bacterium Sinorhizobium meliloti. The RmInt1 intron self-splices in vitro, but this reaction generates side products due to a predicted cryptic IBS1* sequence within the 3' exon. We engineered an RmInt1 intron lacking the cryptic IBS1* sequence, which improved the fidelity of the splicing reaction. However, atypical circular forms of similar electrophoretic mobility to the lariat intron were nevertheless observed. We analyzed a run of four cytidine residues at the 3' splice site potentially responsible for a lack of fidelity at this site leading to the formation of circular intron forms. We showed that mutations of residues base-pairing in the tertiary EBS3-IBS3 interaction increased the efficiency and fidelity of the splicing reaction. Our results indicate that RmInt1 has developed strategies for decreasing its splicing efficiency and fidelity. RmInt1 makes use of unproductive splicing reactions to limit the transposition of the insertion sequence into which it inserts itself in its natural context, thereby preventing potentially harmful dispersion of ISRm2011-2 throughout the genome of its host.
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Affiliation(s)
- Isabel Chillón
- Grupo de Ecología Genética, Estación Experimental del Zaidín, Consejo Superior de Investigaciones Científicas, 18008 Granada, Spain Howard Hughes Medical Institute, Chevy Chase, Maryland 20815, USA
| | - María Dolores Molina-Sánchez
- Grupo de Ecología Genética, Estación Experimental del Zaidín, Consejo Superior de Investigaciones Científicas, 18008 Granada, Spain
| | - Olga Fedorova
- Howard Hughes Medical Institute, Chevy Chase, Maryland 20815, USA Department of Molecular, Cellular and Developmental Biology, Yale University, New Haven, Connecticut 06520, USA
| | - Fernando Manuel García-Rodríguez
- Grupo de Ecología Genética, Estación Experimental del Zaidín, Consejo Superior de Investigaciones Científicas, 18008 Granada, Spain
| | - Francisco Martínez-Abarca
- Grupo de Ecología Genética, Estación Experimental del Zaidín, Consejo Superior de Investigaciones Científicas, 18008 Granada, Spain
| | - Nicolás Toro
- Grupo de Ecología Genética, Estación Experimental del Zaidín, Consejo Superior de Investigaciones Científicas, 18008 Granada, Spain
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20
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Martínez-Rodríguez L, García-Rodríguez FM, Molina-Sánchez MD, Toro N, Martínez-Abarca F. Insights into the strategies used by related group II introns to adapt successfully for the colonisation of a bacterial genome. RNA Biol 2014; 11:1061-71. [PMID: 25482895 PMCID: PMC4615759 DOI: 10.4161/rna.32092] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/23/2023] Open
Abstract
Group II introns are self-splicing RNAs and site-specific mobile retroelements found in bacterial and organellar genomes. The group II intron RmInt1 is present at high copy number in Sinorhizobium meliloti species, and has a multifunctional intron-encoded protein (IEP) with reverse transcriptase/maturase activities, but lacking the DNA-binding and endonuclease domains. We characterized two RmInt1-related group II introns RmInt2 from S. meliloti strain GR4 and Sr.md.I1 from S. medicae strain WSM419 in terms of splicing and mobility activities. We used both wild-type and engineered intron-donor constructs based on ribozyme ΔORF-coding sequence derivatives, and we determined the DNA target requirements for RmInt2, the element most distantly related to RmInt1. The excision and mobility patterns of intron-donor constructs expressing different combinations of IEP and intron RNA provided experimental evidence for the co-operation of IEPs and intron RNAs from related elements in intron splicing and, in some cases, in intron homing. We were also able to identify the DNA target regions recognized by these IEPs lacking the DNA endonuclease domain. Our results provide new insight into the versatility of related group II introns and the possible co-operation between these elements to facilitate the colonization of bacterial genomes.
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Affiliation(s)
- Laura Martínez-Rodríguez
- a Grupo de Ecología Genética; Estación Experimental del Zaidín; Consejo Superior de Investigaciones Científicas ; Granada , Spain
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21
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Nisa-Martínez R, Laporte P, Jiménez-Zurdo JI, Frugier F, Crespi M, Toro N. Localization of a bacterial group II intron-encoded protein in eukaryotic nuclear splicing-related cell compartments. PLoS One 2013; 8:e84056. [PMID: 24391881 PMCID: PMC3877140 DOI: 10.1371/journal.pone.0084056] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/14/2013] [Accepted: 11/15/2013] [Indexed: 11/18/2022] Open
Abstract
Some bacterial group II introns are widely used for genetic engineering in bacteria, because they can be reprogrammed to insert into the desired DNA target sites. There is considerable interest in developing this group II intron gene targeting technology for use in eukaryotes, but nuclear genomes present several obstacles to the use of this approach. The nuclear genomes of eukaryotes do not contain group II introns, but these introns are thought to have been the progenitors of nuclear spliceosomal introns. We investigated the expression and subcellular localization of the bacterial RmInt1 group II intron-encoded protein (IEP) in Arabidopsis thaliana protoplasts. Following the expression of translational fusions of the wild-type protein and several mutant variants with EGFP, the full-length IEP was found exclusively in the nucleolus, whereas the maturase domain alone targeted EGFP to nuclear speckles. The distribution of the bacterial RmInt1 IEP in plant cell protoplasts suggests that the compartmentalization of eukaryotic cells into nucleus and cytoplasm does not prevent group II introns from invading the host genome. Furthermore, the trafficking of the IEP between the nucleolus and the speckles upon maturase inactivation is consistent with the hypothesis that the spliceosomal machinery evolved from group II introns.
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Affiliation(s)
- Rafael Nisa-Martínez
- Consejo Superior de Investigaciones Científicas, Estación Experimental del Zaidín Grupo de Ecología Genética, Granada, Spain
| | - Philippe Laporte
- Centre National de la Recherche Scientifique, Institut des Sciences du Végétal, Gif-sur-Yvette, France
| | - José Ignacio Jiménez-Zurdo
- Consejo Superior de Investigaciones Científicas, Estación Experimental del Zaidín Grupo de Ecología Genética, Granada, Spain
| | - Florian Frugier
- Centre National de la Recherche Scientifique, Institut des Sciences du Végétal, Gif-sur-Yvette, France
| | - Martin Crespi
- Centre National de la Recherche Scientifique, Institut des Sciences du Végétal, Gif-sur-Yvette, France
| | - Nicolás Toro
- Centre National de la Recherche Scientifique, Institut des Sciences du Végétal, Gif-sur-Yvette, France
- * E-mail:
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22
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Dalby SJ, Bonen L. Impact of low temperature on splicing of atypical group II introns in wheat mitochondria. Mitochondrion 2013; 13:647-55. [PMID: 24056090 DOI: 10.1016/j.mito.2013.09.001] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/21/2013] [Revised: 08/14/2013] [Accepted: 09/06/2013] [Indexed: 12/31/2022]
Abstract
To investigate the impact of cold on group II intron splicing, we compared the physical forms of excised mitochondrial introns from wheat embryos germinated at room temperature and 4°C. For introns which deviate from the conventional branchpoint structure, we observed predominantly heterogeneous circularized introns in the cold rather than linear polyadenylated forms arising from a hydrolytic pathway as seen at room temperature. In addition, intron-containing precursors are elevated relative to mature mRNAs upon cold treatment. Our findings indicate that low temperature growth not only reduces splicing efficiency, but also shifts the splicing biochemistry of atypical group II introns to novel, yet productive, pathways.
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Affiliation(s)
- Stephen J Dalby
- Biology Department, University of Ottawa, Ottawa K1N 6N5, Canada
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23
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Nagy V, Pirakitikulr N, Zhou KI, Chillón I, Luo J, Pyle AM. Predicted group II intron lineages E and F comprise catalytically active ribozymes. RNA (NEW YORK, N.Y.) 2013; 19:1266-1278. [PMID: 23882113 PMCID: PMC3753933 DOI: 10.1261/rna.039123.113] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 03/14/2013] [Accepted: 06/12/2013] [Indexed: 06/02/2023]
Abstract
Group II introns are self-splicing, retrotransposable ribozymes that contribute to gene expression and evolution in most organisms. The ongoing identification of new group II introns and recent bioinformatic analyses have suggested that there are novel lineages, which include the group IIE and IIF introns. Because the function and biochemical activity of group IIE and IIF introns have never been experimentally tested and because these introns appear to have features that distinguish them from other introns, we set out to determine if they were indeed self-splicing, catalytically active RNA molecules. To this end, we transcribed and studied a set of diverse group IIE and IIF introns, quantitatively characterizing their in vitro self-splicing reactivity, ionic requirements, and reaction products. In addition, we used mutational analysis to determine the relative role of the EBS-IBS 1 and 2 recognition elements during splicing by these introns. We show that group IIE and IIF introns are indeed distinct active intron families, with different reactivities and structures. We show that the group IIE introns self-splice exclusively through the hydrolytic pathway, while group IIF introns can also catalyze transesterifications. Intriguingly, we observe one group IIF intron that forms circular intron. Finally, despite an apparent EBS2-IBS2 duplex in the sequences of these introns, we find that this interaction plays no role during self-splicing in vitro. It is now clear that the group IIE and IIF introns are functional ribozymes, with distinctive properties that may be useful for biotechnological applications, and which may contribute to the biology of host organisms.
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Affiliation(s)
- Vivien Nagy
- Department of Molecular, Cellular and Developmental Biology, Yale University, New Haven, Connecticut 06520, USA
| | - Nathan Pirakitikulr
- Department of Molecular, Cellular and Developmental Biology, Yale University, New Haven, Connecticut 06520, USA
| | - Katherine Ismei Zhou
- Department of Molecular Biophysics and Biochemistry, Yale University, New Haven, Connecticut 06520, USA
| | - Isabel Chillón
- Department of Molecular, Cellular and Developmental Biology, Yale University, New Haven, Connecticut 06520, USA
- Howard Hughes Medical Institute, Chevy Chase, Maryland 20815, USA
| | - Jerome Luo
- Department of Molecular Biophysics and Biochemistry, Yale University, New Haven, Connecticut 06520, USA
| | - Anna Marie Pyle
- Department of Molecular, Cellular and Developmental Biology, Yale University, New Haven, Connecticut 06520, USA
- Howard Hughes Medical Institute, Chevy Chase, Maryland 20815, USA
- Department of Chemistry, Yale University, New Haven, Connecticut 06520, USA
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24
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Lambowitz AM, Zimmerly S. Group II introns: mobile ribozymes that invade DNA. Cold Spring Harb Perspect Biol 2011; 3:a003616. [PMID: 20463000 DOI: 10.1101/cshperspect.a003616] [Citation(s) in RCA: 298] [Impact Index Per Article: 22.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
Group II introns are mobile ribozymes that self-splice from precursor RNAs to yield excised intron lariat RNAs, which then invade new genomic DNA sites by reverse splicing. The introns encode a reverse transcriptase that stabilizes the catalytically active RNA structure for forward and reverse splicing, and afterwards converts the integrated intron RNA back into DNA. The characteristics of group II introns suggest that they or their close relatives were evolutionary ancestors of spliceosomal introns, the spliceosome, and retrotransposons in eukaryotes. Further, their ribozyme-based DNA integration mechanism enabled the development of group II introns into gene targeting vectors ("targetrons"), which have the unique feature of readily programmable DNA target specificity.
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Affiliation(s)
- Alan M Lambowitz
- Institute for Cellular and Molecular Biology, Department of Chemistry and Biochemistry, University of Texas at Austin, Austin, Texas 78712, USA.
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25
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Chee GJ, Takami H. Alternative splicing by participation of the group II intron ORF in extremely halotolerant and alkaliphilic Oceanobacillus iheyensis. Microbes Environ 2011; 26:54-60. [PMID: 21487203 DOI: 10.1264/jsme2.me10154] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
Group II introns inserted into genes often undergo splicing at unexpected sites, and participate in the transcription of host genes. We identified five copies of a group II intron, designated Oi.Int, in the genome of an extremely halotolerant and alkaliphilic bacillus, Oceanobacillus iheyensis. The Oi.Int4 differs from the Oi.Int3 at four bases. The ligated exons of the Oi.Int4 could not be detected by RT-PCR assays in vivo or in vitro although group II introns can generally self-splice in vitro without the involvement of an intron-encoded open reading frame (ORF). In the Oi.Int4 mutants with base substitutions within the ORF, ligated exons were detected by in vitro self-splicing. It was clear that the ligation of exons during splicing is affected by the sequence of the intron-encoded ORF since the splice sites corresponded to the joining sites of the intron. In addition, the mutant introns showed unexpected multiple products with alternative 5' splice sites. These findings imply that alternative 5' splicing which causes a functional change of ligated exons presumably has influenced past adaptations of O. iheyensis to various environmental changes.
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Affiliation(s)
- Gab-Joo Chee
- Microbial Genome Research Group, Japan Agency for Marine-Earth Science and Technology, 2–15 Natsushima, Yokosuka 237–0061, Japan.
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26
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Molina-Sánchez MD, Barrientos-Durán A, Toro N. Relevance of the branch point adenosine, coordination loop, and 3' exon binding site for in vivo excision of the Sinorhizobium meliloti group II intron RmInt1. J Biol Chem 2011; 286:21154-63. [PMID: 21521690 DOI: 10.1074/jbc.m110.210013] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Excision of the bacterial group II intron RmInt1 has been demonstrated in vivo, resulting in the formation of both intron lariat and putative intron RNA circles. We show here that the bulged adenosine in domain VI of RmInt1 is required for splicing via the branching pathway, but branch site mutants produce small numbers of RNA molecules in which the first G residue of the intron is linked to the last C residue. Mutations in the coordination loop in domain I reduced splicing efficiency, but branched templates clearly predominated among splicing products. We also found that a single substitution at the EBS3 position (G329C), preventing EBS3-IBS3 pairing, resulted in the production of 50 to 100 times more RNA molecules in which the 5' and 3' extremities were joined. We provide evidence that these intron molecules may correspond to both, intron circles linked by a 2'-5' phosphodiester bond, and tandem, head-to-tail intron copies.
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Affiliation(s)
- María Dolores Molina-Sánchez
- Grupo de Ecología Genética, Estación Experimental del Zaidín, Consejo Superior de Investigaciones Científicas, Calle Profesor Albareda 1, 18008 Granada, Spain
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27
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Chillón I, Martínez-Abarca F, Toro N. Splicing of the Sinorhizobium meliloti RmInt1 group II intron provides evidence of retroelement behavior. Nucleic Acids Res 2010; 39:1095-104. [PMID: 20876688 PMCID: PMC3035460 DOI: 10.1093/nar/gkq847] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
Group II introns act as both large catalytic RNAs and mobile retroelements. They are found in organelle and bacterial genomes and are spliced via a lariat intermediate, in a mechanism similar to that of spliceosomal introns. However, their distribution and insertion patterns, particularly for bacterial group II introns, suggest that they function and behave more like retroelements than organelle introns. RmInt1 is an efficient mobile intron found within the ISRm2011-2 insertion sequence in the symbiotic bacterium Sinorhizobium meliloti. This group II intron is excised, in vivo and in vitro, as intron lariats. However, the complete splicing reaction in vivo remains to be elucidated. A lacZ reporter gene system, northern blotting and real-time reverse transcription were carried out to investigate RmInt1 splicing activity. Splicing efficiency of 0.07 ± 0.02% was recorded. These findings suggest that bacterial group II introns function more like retroelements than spliceosomal introns. Their location is consistent with a role for these introns in preventing the spread of other potentially harmful mobile elements in bacteria.
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Affiliation(s)
- Isabel Chillón
- Grupo de Ecología Genética, Estación Experimental del Zaidín, Consejo Superior de Investigaciones Científicas, Calle Profesor Albareda 1, 18008 Granada, Spain
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28
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Pyle AM. The tertiary structure of group II introns: implications for biological function and evolution. Crit Rev Biochem Mol Biol 2010; 45:215-32. [PMID: 20446804 DOI: 10.3109/10409231003796523] [Citation(s) in RCA: 101] [Impact Index Per Article: 7.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
Group II introns are some of the largest ribozymes in nature, and they are a major source of information about RNA assembly and tertiary structural organization. These introns are of biological significance because they are self-splicing mobile elements that have migrated into diverse genomes and played a major role in the genomic organization and metabolism of most life forms. The tertiary structure of group II introns has been the subject of many phylogenetic, genetic, biochemical and biophysical investigations, all of which are consistent with the recent crystal structure of an intact group IIC intron from the alkaliphilic eubacterium Oceanobacillus iheyensis. The crystal structure reveals that catalytic intron domain V is enfolded within the other intronic domains through an elaborate network of diverse tertiary interactions. Within the folded core, DV adopts an activated conformation that readily binds catalytic metal ions and positions them in a manner appropriate for reaction with nucleic acid targets. The tertiary structure of the group II intron reveals new information on motifs for RNA architectural organization, mechanisms of group II intron catalysis, and the evolutionary relationships among RNA processing systems. Guided by the structure and the wealth of previous genetic and biochemical work, it is now possible to deduce the probable location of DVI and the site of additional domains that contribute to the function of the highly derived group IIB and IIA introns.
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Affiliation(s)
- Anna Marie Pyle
- Department of Molecular Biophysics and Biochemistry, Howard Hughes Medical Institute and Yale University, New Haven, CT, USA.
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29
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Molina-Sánchez MD, Martínez-Abarca F, Toro N. Structural features in the C-terminal region of the Sinorhizobium meliloti RmInt1 group II intron-encoded protein contribute to its maturase and intron DNA-insertion function. FEBS J 2009; 277:244-54. [PMID: 19951359 DOI: 10.1111/j.1742-4658.2009.07478.x] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Group II introns are both catalytic RNAs and mobile retroelements that move through a process catalyzed by a RNP complex consisting of an intron-encoded protein and the spliced intron lariat RNA. Group II intron-encoded proteins are multifunctional and contain an N-terminal reverse transcriptase domain, followed by a putative RNA-binding domain (domain X) associated with RNA splicing or maturase activity and a C-terminal DNA binding/DNA endonuclease region. The intron-encoded protein encoded by the mobile group II intron RmInt1, which lacks the DNA binding/DNA endonuclease region, has only a short C-terminal extension (C-tail) after a typical domain X, apparently unrelated to the C-terminal regions of other group II intron-encoded proteins. Multiple sequence alignments identified features of the C-terminal portion of the RmInt1 intron-encoded protein that are conserved throughout evolution in the bacterial ORF class D, suggesting a group-specific functionally important protein region. The functional importance of these features was demonstrated by analyses of deletions and mutations affecting conserved amino acid residues. We found that the C-tail of the RmInt1 intron-encoded protein contributes to the maturase function of this reverse transcriptase protein. Furthermore, within the C-terminal region, we identified, in a predicted alpha-helical region and downstream, conserved residues that are specifically required for the insertion of the intron into DNA targets in the orientation that would make it possible to use the nascent leading strand as a primer. These findings suggest that these group II intron intron-encoded proteins may have adapted to function in mobility by different mechanisms to make use of either leading or lagging-oriented targets in the absence of an endonuclease domain.
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Affiliation(s)
- María D Molina-Sánchez
- Grupo de Ecología Genética, Estación Experimental del Zaidín, Consejo Superior de Investigaciones Científicas, Granada, Spain
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30
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Bonen L. Cis- and trans-splicing of group II introns in plant mitochondria. Mitochondrion 2007; 8:26-34. [PMID: 18006386 DOI: 10.1016/j.mito.2007.09.005] [Citation(s) in RCA: 182] [Impact Index Per Article: 10.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/12/2007] [Revised: 09/12/2007] [Accepted: 09/16/2007] [Indexed: 11/18/2022]
Abstract
Group II-type introns in the mitochondrial genes of flowering plants belong to the ribozymic, mobile retroelement family, but not all exhibit conventional structural features and some follow unusual splicing pathways. Moreover, several introns have been disrupted by DNA rearrangements, so that separately-transcribed precursors undergo splicing in trans. RNA processing in plant mitochondria has the added complexity of C-to-U RNA editing which also sometimes occurs within core intron structures or at exon sites very close to introns. It appears that mitochondrial introns in flowering plants have followed quite different evolutionary pathways than other group II introns.
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Affiliation(s)
- Linda Bonen
- Biology Department, University of Ottawa, 30 Marie Curie, Ottawa, Canada K1N 6N5.
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31
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Abstract
Group II introns are both catalytic RNAs (ribozymes) and mobile retroelements that were discovered almost 14 years ago. It has been suggested that eukaryotic mRNA introns might have originated from the group II introns present in the alphaproteobacterial progenitor of the mitochondria. Bacterial group II introns are of considerable interest not only because of their evolutionary significance, but also because they could potentially be used as tools for genetic manipulation in biotechnology and for gene therapy. This review summarizes what is known about the splicing mechanisms and mobility of bacterial group II introns, and describes the recent development of group II intron-based gene-targetting methods. Bacterial group II intron diversity, evolutionary relationships, and behaviour in bacteria are also discussed.
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Affiliation(s)
- Nicolás Toro
- Grupo de Ecología Genética de la Rizosfera, Estación Experimental del Zaidín, Consejo Superior de Investigaciones Científicas, Granada, Spain.
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32
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Stabell FB, Tourasse NJ, Ravnum S, Kolstø AB. Group II intron in Bacillus cereus has an unusual 3' extension and splices 56 nucleotides downstream of the predicted site. Nucleic Acids Res 2007; 35:1612-23. [PMID: 17301069 PMCID: PMC1865049 DOI: 10.1093/nar/gkm031] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
All group II introns known to date fold into six functional domains. However, we recently identified an intron in Bacillus cereus ATCC 10987, B.c.I4, that splices 56 nt downstream of the expected 3′ splice site in vivo (Tourasse et al. 2005, J. Bacteriol., 187, 5437–5451). In this study, we confirmed by ribonuclease protection assay that the 56-bp segment is part of the intron RNA molecule, and computational prediction suggests that it might form a stable stem-loop structure downstream of domain VI. The splicing of B.c.I4 was further investigated both in vivo and in vitro. Lariat formation proceeded primarily by branching at the ordinary bulged adenosine in domain VI without affecting the fidelity of splicing. In addition, the splicing efficiency of the wild-type intron was better than that of a mutant construct deleted of the 56-bp 3′ extension. These results indicate that the intron has apparently adapted to the extra segment, possibly through conformational adjustments. The extraordinary group II intron B.c.I4 harboring an unprecedented extra 3′ segment constitutes a dramatic example of the flexibility and adaptability of group II introns.
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Affiliation(s)
| | | | | | - Anne-Brit Kolstø
- *To whom correspondence should be addressed. +47 22 85 69 23+47 22 84 49 44
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Abstract
Group II introns are large autocatalytic RNAs found in organellar genomes of plants and lower eukaryotes, as well as in some bacterial genomes. Interestingly, these ribozymes share characteristic traits with both spliceosomal introns and non-LTR retrotransposons and may have a common evolutionary ancestor. Furthermore, group II intron features such as structure, folding and catalytic mechanism differ considerably from those of other large ribozymes, making group II introns an attractive model system to gain novel insights into RNA biology and biochemistry. This review explores recent advances in the structural and mechanistic characterization of group II intron architecture and self-splicing.
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Affiliation(s)
- Olga Fedorova
- Howard Hughes Medical Institute, Yale University, New Haven, CT 06520, USA.
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Nisa-Martínez R, Jiménez-Zurdo JI, Martínez-Abarca F, Muñoz-Adelantado E, Toro N. Dispersion of the RmInt1 group II intron in the Sinorhizobium meliloti genome upon acquisition by conjugative transfer. Nucleic Acids Res 2006; 35:214-22. [PMID: 17158161 PMCID: PMC1802570 DOI: 10.1093/nar/gkl1072] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022] Open
Abstract
RmInt1 is a self-splicing and mobile group II intron initially identified in the bacterium Sinorhizobium meliloti, which encodes a reverse transcriptase–maturase (Intron Encoded Protein, IEP) lacking the C-terminal DNA binding (D) and DNA endonuclease domains (En). RmInt1 invades cognate intronless homing sites (ISRm2011-2) by a mechanism known as retrohoming. This work describes how the RmInt1 intron spreads in the S.meliloti genome upon acquisition by conjugation. This process was revealed by using the wild-type intron RmInt1 and engineered intron-donor constructs based on ribozyme coding sequence (ΔORF)-derivatives with higher homing efficiency than the wild-type intron. The data demonstrate that RmInt1 propagates into the S.meliloti genome primarily by retrohoming with a strand bias related to replication of the chromosome and symbiotic megaplasmids. Moreover, we show that when expressed in trans from a separate plasmid, the IEP is able to mobilize genomic ΔORF ribozymes that afterward displayed wild-type levels of retrohoming. Our results contribute to get further understanding of how group II introns spread into bacterial genomes in nature.
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Affiliation(s)
| | | | | | | | - Nicolás Toro
- To whom correspondence should be addressed. Tel: +3 495 818 1600; Fax: +3 495 812 9600;
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