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Keown JR, Carrique L, Nilsson-Payant BE, Fodor E, Grimes JM. Structural characterization of the full-length Hantaan virus polymerase. PLoS Pathog 2024; 20:e1012781. [PMID: 39652621 DOI: 10.1371/journal.ppat.1012781] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/24/2024] [Revised: 12/19/2024] [Accepted: 11/26/2024] [Indexed: 12/21/2024] Open
Abstract
Hantaviridae are a family of segmented negative-sense RNA viruses that contain important human and animal pathogens. Hantaviridae contain a viral RNA-dependent RNA polymerase that replicates and transcribes the viral genome. Here we establish the expression and purification of the polymerase from the Old World Hantaan virus and characterise the structure using Cryo-EM. We determine a series of structures at resolutions between 2.7 and 3.3 Å of RNA free polymerase comprising the core, core and endonuclease, and a full-length polymerase. The full-length polymerase structure depicts the location of the cap binding and C-terminal domains which are arranged in a conformation that is incompatible with transcription and in a novel conformation not observed in previous conformations of cap-snatching viral polymerases. We further describe structures with 5' vRNA promoter in the presence and absence of a nucleotide triphosphate. The nucleotide bound structure mimics a replication pre-initiation complex and the nucleotide stabilises the motif E in a conformation distinct from those previously observed. We observe motif E in four distinct conformations including β-sheet, two helical arrangements, and nucleotide primed arrangement. The insights gained here guide future mechanistic studies of both the transcription and replication activities of the hantavirus polymerase and for the development of therapeutic targets.
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Affiliation(s)
- Jeremy R Keown
- Division of Structural Biology, Centre for Human Genetics, University of Oxford, Oxford, United Kingdom
- School of Life Sciences, University of Warwick, Coventry, United Kingdom
| | - Loïc Carrique
- Division of Structural Biology, Centre for Human Genetics, University of Oxford, Oxford, United Kingdom
| | - Benjamin E Nilsson-Payant
- Institute for Experimental Virology, TWINCORE Centre for Experimental and Clinical Infection Research, Hannover, Germany
- Cluster of Excellence RESIST (EXC2155), Hannover Medical School, Hannover, Germany
- Department of Microbiology, Tumor and Cell Biology, Karolinska Institutet, Stockholm, Sweden
| | - Ervin Fodor
- Sir William Dunn School of Pathology, University of Oxford, Oxford, United Kingdom
| | - Jonathan M Grimes
- Division of Structural Biology, Centre for Human Genetics, University of Oxford, Oxford, United Kingdom
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2
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Malet H, Williams HM, Cusack S, Rosenthal M. The mechanism of genome replication and transcription in bunyaviruses. PLoS Pathog 2023; 19:e1011060. [PMID: 36634042 PMCID: PMC9836281 DOI: 10.1371/journal.ppat.1011060] [Citation(s) in RCA: 35] [Impact Index Per Article: 17.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/13/2023] Open
Abstract
Bunyaviruses are negative sense, single-strand RNA viruses that infect a wide range of vertebrate, invertebrate and plant hosts. WHO lists three bunyavirus diseases as priority diseases requiring urgent development of medical countermeasures highlighting their high epidemic potential. While the viral large (L) protein containing the RNA-dependent RNA polymerase is a key enzyme in the viral replication cycle and therefore a suitable drug target, our knowledge on the structure and activities of this multifunctional protein has, until recently, been very limited. However, in the last few years, facilitated by the technical advances in the field of cryogenic electron microscopy, many structures of bunyavirus L proteins have been solved. These structures significantly enhance our mechanistic understanding of bunyavirus genome replication and transcription processes and highlight differences and commonalities between the L proteins of different bunyavirus families. Here, we provide a review of our current understanding of genome replication and transcription in bunyaviruses with a focus on the viral L protein. Further, we compare within bunyaviruses and with the related influenza virus polymerase complex and highlight open questions.
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Affiliation(s)
- Hélène Malet
- University Grenoble Alpes, CNRS, CEA, IBS, Grenoble, France
- Institut Universitaire de France (IUF), Paris, France
| | - Harry M. Williams
- Bernhard Nocht Institute for Tropical Medicine (BNITM), Hamburg, Germany
- Centre for Structural Systems Biology, Hamburg, Germany
| | | | - Maria Rosenthal
- Bernhard Nocht Institute for Tropical Medicine (BNITM), Hamburg, Germany
- Centre for Structural Systems Biology, Hamburg, Germany
- Fraunhofer Institute for Translational Medicine and Pharmacology (ITMP), Discovery Research ScreeningPort, Hamburg, Germany
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3
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Pyle JD, Whelan SPJ, Bloyet LM. Structure and function of negative-strand RNA virus polymerase complexes. Enzymes 2021; 50:21-78. [PMID: 34861938 DOI: 10.1016/bs.enz.2021.09.002] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/19/2022]
Abstract
Viruses with negative-strand RNA genomes (NSVs) include many highly pathogenic and economically devastating disease-causing agents of humans, livestock, and plants-highlighted by recent Ebola and measles virus epidemics, and continuously circulating influenza virus. Because of their protein-coding orientation, NSVs face unique challenges for efficient gene expression and genome replication. To overcome these barriers, NSVs deliver a large and multifunctional RNA-dependent RNA polymerase into infected host cells. NSV-encoded polymerases contain all the enzymatic activities required for transcription and replication of their genome-including RNA synthesis and mRNA capping. Here, we review the structures and functions of NSV polymerases with a focus on key domains responsible for viral replication and gene expression. We highlight shared and unique features among polymerases of NSVs from the Mononegavirales, Bunyavirales, and Articulavirales orders.
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Affiliation(s)
- Jesse D Pyle
- Department of Molecular Microbiology, Washington University School of Medicine, St. Louis, MO, United States; Ph.D. Program in Virology, Harvard Medical School, Boston, MA, United States
| | - Sean P J Whelan
- Department of Molecular Microbiology, Washington University School of Medicine, St. Louis, MO, United States.
| | - Louis-Marie Bloyet
- Department of Molecular Microbiology, Washington University School of Medicine, St. Louis, MO, United States.
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4
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Fearns R. Negative‐strand RNA Viruses. Virology 2021. [DOI: 10.1002/9781119818526.ch3] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/21/2022]
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5
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Takenaka-Uema A, Murakami S, Ushio N, Kobayashi-Kitamura T, Uema M, Uchida K, Horimoto T. Generation of a GFP Reporter Akabane Virus with Enhanced Fluorescence Intensity by Modification of Artificial Ambisense S Genome. Viruses 2019; 11:v11070634. [PMID: 31295861 PMCID: PMC6669763 DOI: 10.3390/v11070634] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/10/2019] [Revised: 07/04/2019] [Accepted: 07/09/2019] [Indexed: 11/16/2022] Open
Abstract
We previously generated a recombinant reporter Akabane virus expressing enhanced green fluorescence protein (eGFP-AKAV), with an artificial S genome encoding eGFP in the ambisense RNA. Although the eGFP-AKAV was able to detect infected cells in in vivo histopathological study, its fluorescent signal was too weak to apply to in vivo imaging study. Here, we successfully generated a modified reporter, eGFP/38-AKAV, with 38-nucleotide deletion of the internal region of the 5' untranslated region of S RNA. The eGFP/38-AKAV expressed higher intensity of eGFP fluorescence both in vitro and in vivo than the original eGFP-AKAV did. In addition, eGFP/38-AKAV was pathogenic in mice at a comparable level to that in wild-type AKAV. In the mice infected with eGFP/38-AKAV, the fluorescent signals, i.e., the virus-infected cells, were detected in the central nervous system using the whole-organ imaging. Our findings indicate that eGFP/38-AKAV could be used as a powerful tool to help elucidate the dynamics of AKAV in vivo.
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Affiliation(s)
- Akiko Takenaka-Uema
- Department of Veterinary Microbiology, Graduate School of Agricultural and Life Sciences, The University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo 113-8657, Japan
| | - Shin Murakami
- Department of Veterinary Microbiology, Graduate School of Agricultural and Life Sciences, The University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo 113-8657, Japan
| | - Nanako Ushio
- Department of Veterinary Pathology, Graduate School of Agriculture and Life Sciences, The University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo 113-8657, Japan
| | - Tomoya Kobayashi-Kitamura
- Department of Veterinary Pathology, Graduate School of Agriculture and Life Sciences, The University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo 113-8657, Japan
| | - Masashi Uema
- Division of Biomedical Food Research, National Institute of Health Sciences, 3-25-26 Tonomachi, Kawasaki-ku, Kawasaki 210-9501, Japan
| | - Kazuyuki Uchida
- Department of Veterinary Pathology, Graduate School of Agriculture and Life Sciences, The University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo 113-8657, Japan
| | - Taisuke Horimoto
- Department of Veterinary Microbiology, Graduate School of Agricultural and Life Sciences, The University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo 113-8657, Japan.
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6
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Yadav PD, Nyayanit DA, Shete AM, Jain S, Majumdar TP, Chaubal GY, Shil P, Kore PM, Mourya DT. Complete genome sequencing of Kaisodi virus isolated from ticks in India belonging to Phlebovirus genus, family Phenuiviridae. Ticks Tick Borne Dis 2018; 10:23-33. [PMID: 30181094 DOI: 10.1016/j.ttbdis.2018.08.012] [Citation(s) in RCA: 37] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/04/2018] [Revised: 08/20/2018] [Accepted: 08/27/2018] [Indexed: 11/29/2022]
Abstract
An unknown virus was repeatedly isolated from hard tick (Haemaphysalis spinigera) during a proactive arbovirus survey in ticks conducted in 1957, in India. The virus remained uncharacterized for a long time. The passages of this virus in different vertebrate and invertebrate cells along with human and monkey-derived cell culture showed no cytopathic effect. It was identified later to be a member of Kaisodi group among Phlebovirus genus in the family Phenuiviridae (Order: Bunyavirales) by serological methods. Due to its genomic diversity, sequencing of this virus was a challenge for a while. In this study, we were able to sequence the complete genome of this virus isolate using next-generation sequencing (NGS) platform. The unknown virus was identified to be Kaisodi virus (KASDV) using NGS analysis. De novo genome assembly derived three genomic segments for the KASDV which encode for RNA-dependent RNA polymerase, glycoprotein precursor, and nucleoprotein. Functional as well as conserved domains for Kaisodi serogroup viruses were predicted and compared to a known representative of the genus Phlebovirus. The phylogenetic tree revealed its closeness to Silverwater virus, of Kaisodi serogroup with nucleotide (69%, 62%, and 61%) and amino acid (52%, 51%, and 62%) identity for L, M, and S segment, respectively. The study demonstrates the presence of a conserved motif (72TRGNK76) around the RNA binding motif region in tick-borne phleboviruses. The intergenic region encompassing the S segment of Kaisodi serogroup was GC-rich whereas the other Phlebovirus had AT-rich genome. KASDV has the largest intergenic region and larger loops, suggesting stem-loops formed due to larger loops as a possible factor for instability and cause of transcription termination. This paper also describes the real-time RT-PCR and RT-PCR assays developed and used for the detection of KASDV RNA in ticks from Karnataka, Kerala and Maharashtra State, India. The KASDV positivity observed in the recently collected tick pools indicates that the KASDV, isolated from Karnataka state in 1957, is also circulating in the adjoining Kerala state. On the basis of the current study, it should be possible to develop diagnostic assays which would facilitate an in-depth field survey exploring the veterinary and medical significance of KASDV.
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Affiliation(s)
- P D Yadav
- Maximum Containment Facility, Microbial Containment Complex, ICMR-National Institute of Virology, Sus Road, Pashan, Pune 411021, India
| | - D A Nyayanit
- Maximum Containment Facility, Microbial Containment Complex, ICMR-National Institute of Virology, Sus Road, Pashan, Pune 411021, India
| | - A M Shete
- Maximum Containment Facility, Microbial Containment Complex, ICMR-National Institute of Virology, Sus Road, Pashan, Pune 411021, India
| | - S Jain
- Maximum Containment Facility, Microbial Containment Complex, ICMR-National Institute of Virology, Sus Road, Pashan, Pune 411021, India
| | - T P Majumdar
- Maximum Containment Facility, Microbial Containment Complex, ICMR-National Institute of Virology, Sus Road, Pashan, Pune 411021, India
| | - G Y Chaubal
- Maximum Containment Facility, Microbial Containment Complex, ICMR-National Institute of Virology, Sus Road, Pashan, Pune 411021, India
| | - P Shil
- Maximum Containment Facility, Microbial Containment Complex, ICMR-National Institute of Virology, Sus Road, Pashan, Pune 411021, India
| | - P M Kore
- Maximum Containment Facility, Microbial Containment Complex, ICMR-National Institute of Virology, Sus Road, Pashan, Pune 411021, India
| | - D T Mourya
- Maximum Containment Facility, Microbial Containment Complex, ICMR-National Institute of Virology, Sus Road, Pashan, Pune 411021, India.
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7
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Sun Y, Li J, Gao GF, Tien P, Liu W. Bunyavirales ribonucleoproteins: the viral replication and transcription machinery. Crit Rev Microbiol 2018. [PMID: 29516765 DOI: 10.1080/1040841x.2018.1446901] [Citation(s) in RCA: 46] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/17/2022]
Abstract
The Bunyavirales order is one of the largest groups of segmented negative-sense single-stranded RNA viruses, which includes many pathogenic strains that cause severe human diseases. The RNA segments of the bunyavirus genome are separately encapsidated by multiple copies of nucleoprotein (N), and both termini of each N-encapsidated genomic RNA segment bind to one copy of the viral L polymerase protein. The viral genomic RNA, N and L protein together form the ribonucleoprotein (RNP) complex that constitutes the molecular machinery for viral genome replication and transcription. Recently, breakthroughs have been achieved in understanding the architecture of bunyavirus RNPs with the determination of the atomic structures of the N and L proteins from various members of this order. In this review, we discuss the structures and functions of these bunyavirus RNP components, as well as viral genome replication and transcription mechanisms.
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Affiliation(s)
- Yeping Sun
- a CAS Key Laboratory of Pathogenic Microbiology and Immunology , Institute of Microbiology, Chinese Academy of Sciences , Beijing , China
| | - Jing Li
- a CAS Key Laboratory of Pathogenic Microbiology and Immunology , Institute of Microbiology, Chinese Academy of Sciences , Beijing , China
| | - George F Gao
- a CAS Key Laboratory of Pathogenic Microbiology and Immunology , Institute of Microbiology, Chinese Academy of Sciences , Beijing , China.,b National Institute for Viral Disease Control and Prevention, Chinese Center for Disease Control and Prevention , Beijing , China
| | - Po Tien
- a CAS Key Laboratory of Pathogenic Microbiology and Immunology , Institute of Microbiology, Chinese Academy of Sciences , Beijing , China
| | - Wenjun Liu
- a CAS Key Laboratory of Pathogenic Microbiology and Immunology , Institute of Microbiology, Chinese Academy of Sciences , Beijing , China
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8
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Yanase T, Kato T, Hayama Y, Akiyama M, Itoh N, Horiuchi S, Hirashima Y, Shirafuji H, Yamakawa M, Tanaka S, Tsutsui T. Transition of Akabane virus genogroups and its association with changes in the nature of disease in Japan. Transbound Emerg Dis 2017; 65:e434-e443. [DOI: 10.1111/tbed.12778] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/06/2017] [Indexed: 12/22/2022]
Affiliation(s)
- T. Yanase
- Kyushu Research Station; National Institute of Animal Health; NARO; Kagoshima Japan
| | - T. Kato
- Kyushu Research Station; National Institute of Animal Health; NARO; Kagoshima Japan
| | - Y. Hayama
- Division of Viral Disease and Epidemiology; National Institute of Animal Health; NARO; Ibaraki Japan
| | - M. Akiyama
- Eastern Center for Livestock Hygiene Service; Hiroshima Japan
| | - N. Itoh
- Western Center for Livestock Hygiene Service; Hiroshima Japan
| | - S. Horiuchi
- Miyazaki Livestock Hygiene Service Center; Miyazaki Japan
| | - Y. Hirashima
- Kagoshima Central Livestock Hygiene Service Center; Kagoshima Japan
| | - H. Shirafuji
- Kyushu Research Station; National Institute of Animal Health; NARO; Kagoshima Japan
| | - M. Yamakawa
- Exotic Disease Research Station; National Institute of Animal Health; NARO; Tokyo Japan
| | - S. Tanaka
- Kyushu Research Station; National Institute of Animal Health; NARO; Kagoshima Japan
| | - T. Tsutsui
- Division of Viral Disease and Epidemiology; National Institute of Animal Health; NARO; Ibaraki Japan
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9
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Lwande OW, Bucht G, Ahlm C, Ahlm K, Näslund J, Evander M. Mosquito-borne Inkoo virus in northern Sweden - isolation and whole genome sequencing. Virol J 2017; 14:61. [PMID: 28330505 PMCID: PMC5362992 DOI: 10.1186/s12985-017-0725-5] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/23/2016] [Accepted: 03/08/2017] [Indexed: 11/25/2022] Open
Abstract
BACKGROUND Inkoo virus (INKV) is a less known mosquito-borne virus belonging to Bunyaviridae, genus Orthobunyavirus, California serogroup. Studies indicate that INKV infection is mainly asymptomatic, but can cause mild encephalitis in humans. In northern Europe, the sero-prevalence against INKV is high, 41% in Sweden and 51% in Finland. Previously, INKV RNA has been detected in adult Aedes (Ae.) communis, Ae. hexodontus and Ae. punctor mosquitoes and Ae. communis larvae, but there are still gaps of knowledge regarding mosquito vectors and genetic diversity. Therefore, we aimed to determine the occurrence of INKV in its mosquito vector and characterize the isolates. METHODS About 125,000 mosquitoes were collected during a mosquito-borne virus surveillance in northern Sweden during the summer period of 2015. Of these, 10,000 mosquitoes were processed for virus isolation and detection using cell culture and RT-PCR. Virus isolates were further characterized by whole genome sequencing. Genetic typing of mosquito species was conducted by cytochrome oxidase subunit I (COI) gene amplification and sequencing (genetic barcoding). RESULTS Several Ae. communis mosquitoes were found positive for INKV RNA and two isolates were obtained. The first complete sequences of the small (S), medium (M), and large (L) segments of INKV in Sweden were obtained. Phylogenetic analysis showed that the INKV genome was most closely related to other INKV isolates from Sweden and Finland. Of the three INKV genome segments, the INKV M segment had the highest frequency of non-synonymous mutations. The overall G/C-content of INKV genes was low for the N/NSs genes (43.8-45.5%), polyprotein (Gn/Gc/NSm) gene (35.6%) and the RNA polymerase gene (33.8%) This may be due to the fact that INKV in most instances utilized A or T in the third codon position. CONCLUSIONS INKV is frequently circulating in northern Sweden and Ae. communis is the key vector. The high mutation rate of the INKV M segment may have consequences on virulence.
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Affiliation(s)
| | - Göran Bucht
- Swedish Defence Research Agency, CBRN Defence and Security, Umeå, Sweden
| | - Clas Ahlm
- Department of Clinical Microbiology, Infectious Diseases, Umeå University, Umeå, Sweden
| | - Kristoffer Ahlm
- Department of Clinical Microbiology, Infectious Diseases, Umeå University, Umeå, Sweden
| | - Jonas Näslund
- Swedish Defence Research Agency, CBRN Defence and Security, Umeå, Sweden
| | - Magnus Evander
- Department of Clinical Microbiology, Virology, Umeå University, Umeå, Sweden
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10
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Generation of a Recombinant Akabane Virus Expressing Enhanced Green Fluorescent Protein. J Virol 2015; 89:9477-84. [PMID: 26157127 DOI: 10.1128/jvi.00681-15] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/12/2015] [Accepted: 06/29/2015] [Indexed: 02/01/2023] Open
Abstract
UNLABELLED We generated a recombinant Akabane virus (AKAV) expressing enhanced green fluorescence protein (eGFP-AKAV) by using reverse genetics. We artificially constructed an ambisense AKAV S genome encoding N/NSs on the negative-sense strand, and eGFP on the positive-sense strand with an intergenic region (IGR) derived from the Rift Valley fever virus (RVFV) S genome. The recombinant virus exhibited eGFP fluorescence and had a cytopathic effect in cell cultures, even after several passages. These results indicate that the gene encoding eGFP in the ambisense RNA could be stably maintained. Transcription of N/NSs and eGFP mRNAs of eGFP-AKAV was terminated within the IGR. The mechanism responsible for this appears to be different from that in RVFV, where the termination sites for N and NSs are determined by a defined signal sequence. We inoculated suckling mice intraperitoneally with eGFP-AKAV, which resulted in neurological signs and lethality equivalent to those seen for the parent AKAV. Fluorescence from eGFP in frozen brain slices from the eGFP-AKAV-infected mice was localized to the cerebellum, pons, and medulla oblongata. Our approach to producing a fluorescent virus, using an ambisense genome, helped obtain eGFP-AKAV, a fluorescent bunyavirus whose viral genes are intact and which can be easily visualized. IMPORTANCE AKAV is the etiological agent of arthrogryposis-hydranencephaly syndrome in ruminants, which causes considerable economic loss to the livestock industry. We successfully generated a recombinant enhanced green fluorescent protein-tagged AKAV containing an artificial ambisense S genome. This virus could become a useful tool for analyzing AKAV pathogenesis in host animals. In addition, our approach of using an ambisense genome to generate an orthobunyavirus stably expressing a foreign gene could contribute to establishing alternative vaccine strategies, such as bivalent vaccine virus constructs, for veterinary use against infectious diseases.
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11
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Flexibility of bunyavirus genomes: creation of an orthobunyavirus with an ambisense S segment. J Virol 2015; 89:5525-35. [PMID: 25740985 DOI: 10.1128/jvi.03595-14] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/16/2014] [Accepted: 02/26/2015] [Indexed: 12/28/2022] Open
Abstract
UNLABELLED The Bunyamwera (BUNV) orthobunyavirus NSs protein has proven a challenge to study in the context of viral infection. NSs is encoded in a reading frame that overlaps that of the viral nucleocapsid (N) protein thus limiting options for mutagenesis. In addition, NSs is poorly immunogenic, and antibodies only work in certain techniques while the protein itself is subject to proteasomal degradation. In order to generate a virus that expresses NSs independently of N, an ambisense S RNA segment was designed by mutating the 5'- and 3'-terminal nucleotide sequences. These mutations were previously shown to alter promoter activity so that both replication and transcription were promoted from both the genome and the antigenome RNAs (J. N. Barr et al., J. Virol. 79: 12602-12607, 2005). As proof of principle, a recombinant BUNV was created that expressed green fluorescent protein (GFP) in the ambisense orientation. GFP expression was detected throughout at least 10 passages. Recombinant BUNV encoding epitope-tagged versions of NSs in the ambisense orientation expressed NSs via a subgenomic mRNA, and two viruses grew to titers only modestly lower than parental rBUNdelNSs2 virus. The ambisense viruses were temperature sensitive, and NSs was shown to localize to both the nucleus and the cytoplasm during infection. These viruses will be useful in further studies on structure-function relationships of the orthobunyavirus NSs protein. IMPORTANCE Bunyamwera virus (BUNV) is the type species and model system for both the family Bunyaviridae and the genus Orthobunyavirus, a group that includes many significant human and animal pathogens. Studying the basic molecular biology of these viruses is of great importance to underpin research into vaccines and antivirals. We demonstrate here the plasticity of the BUNV genome by generating recombinant viruses where the normal negative-sense S segment has been converted into an ambisense segment, allowing independent expression of either a foreign gene (green fluorescent protein) or the viral nonstructural NSs protein. These new reagents will allow detailed investigation of NSs, the orthobunyavirus interferon antagonist.
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12
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Abstract
Orthobunyaviruses, which have small, tripartite, negative-sense RNA genomes and structurally simple virions composed of just four proteins, can have devastating effects on human health and well-being, either by causing disease in humans or by causing disease in livestock and crops. In this Review, I describe the recent genetic and structural advances that have revealed important insights into the composition of orthobunyavirus virions, viral transcription and replication and viral interactions with the host innate immune response. Lastly, I highlight outstanding questions and areas of future research.
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Affiliation(s)
- Richard M Elliott
- MRC-University of Glasgow Centre for Virus Research, 464 Bearsden Road, Glasgow G61 1QH, UK
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13
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Coupeau D, Claine F, Wiggers L, Martin B, Kirschvink N, Muylkens B. Characterization of messenger RNA termini in Schmallenberg virus and related Simbuviruses. J Gen Virol 2013; 94:2399-2405. [PMID: 23939979 DOI: 10.1099/vir.0.055954-0] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023] Open
Abstract
Schmallenberg virus (SBV) is an emerging arbovirus infecting ruminants in Europe. SBV belongs to the Bunyaviridae family within the Simbu serogroup. Its genome comprises three segments, small (S), medium (M) and large (L), that together encode six proteins and contain NTRs. NTRs are involved in initiation and termination of transcription and in genome packaging. This study explored the 3' mRNA termini of SBV and related Simbuviruses. In addition, the 5' termini of SBV messenger RNA (mRNA) were characterized. For the three SBV segments, cap-snatching was found to initiate mRNA transcription both in vivo and in vitro. The presence of extraneous nucleotides between host RNA leaders and the viral termini fits with the previously described prime-and-realign theory. At the 3' termini, common features were identified for SBV and related Simbuviruses. However, different patterns were observed for the termini of the three segments from the same virus type.
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Affiliation(s)
- Damien Coupeau
- Veterinary Integrated Research Unit, Faculty of Sciences, Namur Research Institute for Life Sciences, University of Namur, 5000 Namur, Belgium
| | - François Claine
- Veterinary Integrated Research Unit, Faculty of Sciences, Namur Research Institute for Life Sciences, University of Namur, 5000 Namur, Belgium
| | - Laetitia Wiggers
- Veterinary Integrated Research Unit, Faculty of Sciences, Namur Research Institute for Life Sciences, University of Namur, 5000 Namur, Belgium
| | - Beer Martin
- Friedrich-Loeffler-Institut, Greifswald-Insel-Riems, Germany
| | - Nathalie Kirschvink
- Veterinary Integrated Research Unit, Faculty of Sciences, Namur Research Institute for Life Sciences, University of Namur, 5000 Namur, Belgium
| | - Benoît Muylkens
- Veterinary Integrated Research Unit, Faculty of Sciences, Namur Research Institute for Life Sciences, University of Namur, 5000 Namur, Belgium
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14
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Attenuation of bunyamwera orthobunyavirus replication by targeted mutagenesis of genomic untranslated regions and creation of viable viruses with minimal genome segments. J Virol 2012; 86:13672-8. [PMID: 23035233 DOI: 10.1128/jvi.02253-12] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022] Open
Abstract
Bunyamwera virus (BUNV) is the prototype virus for both the genus Orthobunyavirus and the family Bunyaviridae. BUNV has a tripartite, negative-sense RNA genome. The coding region of each segment is flanked by untranslated regions (UTRs) that are partially complementary. The UTRs play an important role in the virus life cycle by promoting transcription, replication, and encapsidation of the viral genome. Using reverse genetics, we generated recombinant viruses that contained deletions within the 3' and/or 5' UTRs of the L or M segments to determine the minimal UTRs competent for virus viability. We then generated viruses carrying deleted UTRs in all three segments. These viruses were grossly attenuated in tissue culture, being significantly impaired in their ability to produce plaques in BHK cells, and had a reduced capacity to cause host cell protein shutoff. After serial passage in tissue culture, some viruses partially recovered fitness, generating higher titers and producing larger plaques. We determined the complete nucleotide sequence for each virus. The deleted UTR sequences were maintained, and no amino acid changes were observed in the nonstructural proteins (NSs and NSm), the nucleocapsid protein (N), or the Gn glycoprotein. One virus had a single amino acid substitution in Gc. Three viruses contained amino acid changes in the viral polymerase that mostly occurred in the C-terminal domain of the L protein. Although the role of this domain remains unknown, we suggest that those changes might be involved in the evolution of the polymerase to recognize the deleted UTRs more efficiently.
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