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Stafford KA, Trbovic N, Butterwick JA, Abel R, Friesner RA, Palmer AG. Conformational preferences underlying reduced activity of a thermophilic ribonuclease H. J Mol Biol 2014; 427:853-866. [PMID: 25550198 DOI: 10.1016/j.jmb.2014.11.023] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/25/2014] [Accepted: 11/14/2014] [Indexed: 11/30/2022]
Abstract
The conformational basis for reduced activity of the thermophilic ribonuclease HI enzyme from Thermus thermophilus, compared to its mesophilic homolog from Escherichia coli, is elucidated using a combination of NMR spectroscopy and molecular dynamics (MD) simulations. Explicit-solvent all-atom MD simulations of the two wild-type proteins and an E. coli mutant in which a glycine residue is inserted after position 80 to mimic the T. thermophilus protein reproduce the differences in conformational dynamics determined from (15)N spin-relaxation NMR spectroscopy of three loop regions that surround the active site and contain functionally important residues: the glycine-rich region, the handle region, and the β5/αE loop. Examination of the MD trajectories indicates that the thermophilic protein samples conformations productive for substrate binding and activity less frequently than the mesophilic enzyme, although these differences may manifest as either increased or decreased relative flexibility of the different regions. Additional MD simulations indicate that mutations increasing activity of the T. thermophilus enzyme at mesophilic temperatures do so by reconfiguring the local environments of the mutated sites to more closely resemble active conformations. Taken together, the results show that both locally increased and decreased flexibility contribute to an overall reduction in activity of T. thermophilus ribonuclease H compared to its mesophilic E. coli homolog.
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Affiliation(s)
- Kate A Stafford
- Department of Biochemistry and Molecular Biophysics, Columbia University, New York, NY 10032, USA
| | - Nikola Trbovic
- Department of Biochemistry and Molecular Biophysics, Columbia University, New York, NY 10032, USA
| | - Joel A Butterwick
- Department of Biochemistry and Molecular Biophysics, Columbia University, New York, NY 10032, USA
| | - Robert Abel
- Department of Chemistry, Columbia University, New York, NY 10027, USA
| | | | - Arthur G Palmer
- Department of Biochemistry and Molecular Biophysics, Columbia University, New York, NY 10032, USA.
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Lampson BC, Inouye M, Inouye S. Retrons, msDNA, and the bacterial genome. Cytogenet Genome Res 2005; 110:491-9. [PMID: 16093702 DOI: 10.1159/000084982] [Citation(s) in RCA: 66] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/09/2003] [Accepted: 10/16/2003] [Indexed: 12/23/2022] Open
Abstract
Retrons are distinct DNA sequences that code for a reverse transcriptase (RT) similar to the RTs produced by retroviruses and other types of retroelements. Retron DNAs are commonly associated with prophage DNA and are found in the genomes of a wide variety of different bacteria. The retron RT is used to synthesize a strange satellite DNA known as msDNA. msDNA is actually a complex of DNA, RNA, and probably protein. It is composed of a small, single-stranded DNA, linked to a small, single-stranded RNA molecule. The 5' end of the DNA molecule is joined to an internal guanosine residue of the RNA molecule by a unique 2'-5' phosphodiester bond. msDNA is produced in many hundreds of copies per cell, but its function remains unknown. Although retrons are absent from the genome of most members of a population of related bacteria, retrons may not be entirely benign DNAs. Evidence is beginning to suggest that retron elements may produce small but potentially significant effects on the host cell. This includes the generation of repeated copies of the msDNA sequence in the genome, and increasing the frequency of spontaneous mutations. Because these events involve the retron RT, this may represent a source of reverse transcription in the bacterial cell. Thus, the process of reverse transcription, a force that has profoundly affected the content and structure of most eukaryotic genomes, may likewise be responsible for changes in some prokaryotic genomes.
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Affiliation(s)
- B C Lampson
- Department of Health Sciences, East Tennessee State University, Johnson City, TN, USA
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Malik HS. Ribonuclease H evolution in retrotransposable elements. Cytogenet Genome Res 2005; 110:392-401. [PMID: 16093691 DOI: 10.1159/000084971] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/12/2004] [Accepted: 02/11/2004] [Indexed: 11/19/2022] Open
Abstract
Eukaryotic and prokaryotic genomes encode either Type I or Type II Ribonuclease H (RNH) which is important for processing RNA primers that prime DNA replication in almost all organisms. This review highlights the important role that Type I RNH plays in the life cycle of many retroelements, and its utility in tracing early events in retroelement evolution. Many retroelements utilize host genome-encoded RNH, but several lineages of retroelements, including some non-LTR retroposons and all LTR retrotransposons, encode their own RNH domains. Examination of these RNH domains suggests that all LTR retrotransposons acquired an enzymatically weak RNH domain that is missing an important catalytic residue found in all other RNH enzymes. We propose that this reduced activity is essential to ensure correct processing of the polypurine tract (PPT), which is an important step in the life cycle of these retrotransposons. Vertebrate retroviruses appear to have reacquired their RNH domains, which are catalytically more active, but their ancestral RNH domains (found in other LTR retrotransposons) have degenerated to give rise to the tether domains unique to vertebrate retroviruses. The tether domain may serve to control the more active RNH domain of vertebrate retroviruses. Phylogenetic analysis of the RNH domains is also useful to "date" the relative ages of LTR and non-LTR retroelements. It appears that all LTR retrotransposons are as old as, or younger than, the "youngest" lineages of non-LTR retroelements, suggesting that LTR retrotransposons arose late in eukaryotes.
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Affiliation(s)
- H S Malik
- Basic Sciences, Fred Hutchinson Cancer Research Center, Seattle, WA 98109-1024, USA.
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Lampson B, Inouye M, Inouye S. The msDNAs of bacteria. PROGRESS IN NUCLEIC ACID RESEARCH AND MOLECULAR BIOLOGY 2001; 67:65-91. [PMID: 11525386 DOI: 10.1016/s0079-6603(01)67025-9] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/16/2023]
Abstract
msDNAs are small, structurally unique satellite DNAs found in a number of Gram-negative bacteria. Composed of hundreds of copies of single-stranded DNA--hence the name multicopy single-stranded DNA--msDNA is actually a complex of DNA, RNA, and probably protein. These peculiar molecules are synthesized by a reverse transcription mechanism catalyzed by a reverse transcriptase (RT) that is evolutionarily related to the polymerase found in the HIV virus. The genes, including the RT gene, responsible for the synthesis of msDNA are encoded in a retron, a genetic element that is carried on the bacterial chromosome. The retron is, in fact, the first such retroelement to be discovered in prokaryotic cells. This report is a comprehensive review of the many interesting questions raised by this unique DNA and the fascinating answers it has revealed. We have learned a great deal about the structure of msDNA: how it is synthesized, the structure and functions of the RT protein required to make it, its effects on the host cell, the retron element that encodes it, its possible origins and evolution, and even its potential usefulness as a practical genetic tool. Despite the impressive gains in our understanding of the msDNAs, however, the simple, fundamental question of its natural function remains an enduring mystery. Thus, we have much more to learn about the msDNAs of bacteria.
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MESH Headings
- Bacteria/enzymology
- Bacteria/genetics
- Base Sequence
- DNA, Bacterial/biosynthesis
- DNA, Bacterial/chemistry
- DNA, Bacterial/genetics
- DNA, Single-Stranded/biosynthesis
- DNA, Single-Stranded/chemistry
- DNA, Single-Stranded/genetics
- Evolution, Molecular
- Molecular Sequence Data
- RNA, Bacterial/biosynthesis
- RNA, Bacterial/chemistry
- RNA, Bacterial/genetics
- RNA-Directed DNA Polymerase/metabolism
- Transcription, Genetic
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Affiliation(s)
- B Lampson
- Department of Health Sciences, East Tennessee State University, Johnson City 37614, USA
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Abstract
This map is an update of the edition 9 map by Berlyn et al. (M. K. B. Berlyn, K. B. Low, and K. E. Rudd, p. 1715-1902, in F. C. Neidhardt et al., ed., Escherichia coli and Salmonella: cellular and molecular biology, 2nd ed., vol. 2, 1996). It uses coordinates established by the completed sequence, expressed as 100 minutes for the entire circular map, and adds new genes discovered and established since 1996 and eliminates those shown to correspond to other known genes. The latter are included as synonyms. An alphabetical list of genes showing map location, synonyms, the protein or RNA product of the gene, phenotypes of mutants, and reference citations is provided. In addition to genes known to correspond to gene sequences, other genes, often older, that are described by phenotype and older mapping techniques and that have not been correlated with sequences are included.
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Affiliation(s)
- M K Berlyn
- Department of Biology and School of Forestry and Environmental Studies, Yale University, New Haven, Connecticut 06520-8104, USA.
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Kim K, Jeong D, Lim D. A mutational study of the site-specific cleavage of EC83, a multicopy single-stranded DNA (msDNA): nucleotides at the msDNA stem are important for its cleavage. J Bacteriol 1997; 179:6518-21. [PMID: 9335306 PMCID: PMC179573 DOI: 10.1128/jb.179.20.6518-6521.1997] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
Multicopy single-stranded DNA (msDNA) molecules consist of single-stranded DNA covalently linked to RNA. Such molecules are encoded by genetic elements called retrons. Unlike other retrons, retron EC83 isolated from Escherichia coli 161 produces RNA-free msDNA by site-specific cleavage of msDNA at 5'-TTGA/A-3', where the slash indicates the cleavage site. In order to investigate factors responsible for the msDNA cleavage, retron EC83 was treated with hydroxylamine and colonies were screened for cleavage-negative mutants. We isolated three mutants which were defective in msDNA cleavage and produced RNA-linked msDNA. They were all affected in msd, a gene for msDNA, with a base substitution at the bottom part of the msDNA stem. In contrast, base substitution at and around the cleavage site has no marked effect on msDNA synthesis or its cleavage. From these results, we concluded that the nucleotides at the bottom of the msDNA stem, but not the nucleotides at the cleavage site, play a major role in the recognition and cleavage of msDNA EC83.
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Affiliation(s)
- K Kim
- Department of Microbiology, Gyeongsang National University, Gazwadong, Chinju, Korea
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Abstract
Using a sensitive primer extension technique, we have carried out studies to localize the start site of replication of the replicon RepFIC. In the course of these studies, we have found evidence that supports the hypothesis that transcription is an integral component of the initiation of replication. On the basis of our findings, we suggest that the transcript is processed to act as a primer, and therefore we propose that the transcript has a dual role as primer of replication and mRNA for the RepA1 protein. We present a model, based on our evidence, for the initiation of replication of the replicon RepFIC. This model provides as well an alternative explanation for what has been called the cis action of RepA1, and we show that RepA1 may act in trans as well as in cis.
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Affiliation(s)
- R Maas
- Department of Microbiology, New York University Medical Center, New York 10016, USA.
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