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René B, Mauffret O, Fossé P. Retroviral nucleocapsid proteins and DNA strand transfers. BIOCHIMIE OPEN 2018; 7:10-25. [PMID: 30109196 PMCID: PMC6088434 DOI: 10.1016/j.biopen.2018.07.001] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 05/07/2018] [Accepted: 07/08/2018] [Indexed: 12/12/2022]
Abstract
An infectious retroviral particle contains 1000-1500 molecules of the nucleocapsid protein (NC) that cover the diploid RNA genome. NC is a small zinc finger protein that possesses nucleic acid chaperone activity that enables NC to rearrange DNA and RNA molecules into the most thermodynamically stable structures usually those containing the maximum number of base pairs. Thanks to the chaperone activity, NC plays an essential role in reverse transcription of the retroviral genome by facilitating the strand transfer reactions of this process. In addition, these reactions are involved in recombination events that can generate multiple drug resistance mutations in the presence of anti-HIV-1 drugs. The strand transfer reactions rely on base pairing of folded DNA/RNA structures. The molecular mechanisms responsible for NC-mediated strand transfer reactions are presented and discussed in this review. Antiretroviral strategies targeting the NC-mediated strand transfer events are also discussed.
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Affiliation(s)
- Brigitte René
- LBPA, ENS Paris-Saclay, UMR 8113, CNRS, Université Paris-Saclay, 61 Avenue du Président Wilson, 94235, Cachan, France
| | - Olivier Mauffret
- LBPA, ENS Paris-Saclay, UMR 8113, CNRS, Université Paris-Saclay, 61 Avenue du Président Wilson, 94235, Cachan, France
| | - Philippe Fossé
- LBPA, ENS Paris-Saclay, UMR 8113, CNRS, Université Paris-Saclay, 61 Avenue du Président Wilson, 94235, Cachan, France
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2
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Post K, Olson ED, Naufer MN, Gorelick RJ, Rouzina I, Williams MC, Musier-Forsyth K, Levin JG. Mechanistic differences between HIV-1 and SIV nucleocapsid proteins and cross-species HIV-1 genomic RNA recognition. Retrovirology 2016; 13:89. [PMID: 28034301 PMCID: PMC5198506 DOI: 10.1186/s12977-016-0322-5] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/23/2016] [Accepted: 11/29/2016] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND The nucleocapsid (NC) domain of HIV-1 Gag is responsible for specific recognition and packaging of genomic RNA (gRNA) into new viral particles. This occurs through specific interactions between the Gag NC domain and the Psi packaging signal in gRNA. In addition to this critical function, NC proteins are also nucleic acid (NA) chaperone proteins that facilitate NA rearrangements during reverse transcription. Although the interaction with Psi and chaperone activity of HIV-1 NC have been well characterized in vitro, little is known about simian immunodeficiency virus (SIV) NC. Non-human primates are frequently used as a platform to study retroviral infection in vivo; thus, it is important to understand underlying mechanistic differences between HIV-1 and SIV NC. RESULTS Here, we characterize SIV NC chaperone activity for the first time. Only modest differences are observed in the ability of SIV NC to facilitate reactions that mimic the minus-strand annealing and transfer steps of reverse transcription relative to HIV-1 NC, with the latter displaying slightly higher strand transfer and annealing rates. Quantitative single molecule DNA stretching studies and dynamic light scattering experiments reveal that these differences are due to significantly increased DNA compaction energy and higher aggregation capability of HIV-1 NC relative to the SIV protein. Using salt-titration binding assays, we find that both proteins are strikingly similar in their ability to specifically interact with HIV-1 Psi RNA. In contrast, they do not demonstrate specific binding to an RNA derived from the putative SIV packaging signal. CONCLUSIONS Based on these studies, we conclude that (1) HIV-1 NC is a slightly more efficient NA chaperone protein than SIV NC, (2) mechanistic differences between the NA interactions of highly similar retroviral NC proteins are revealed by quantitative single molecule DNA stretching, and (3) SIV NC demonstrates cross-species recognition of the HIV-1 Psi RNA packaging signal.
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Affiliation(s)
- Klara Post
- Section on Viral Gene Regulation, Program in Genomics of Differentiation, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD 20892-2780 USA
| | - Erik D. Olson
- Department of Chemistry and Biochemistry, Center for Retrovirus Research, and Center for RNA Biology, The Ohio State University, Columbus, OH 43210 USA
| | - M. Nabuan Naufer
- Department of Physics, Northeastern University, Boston, MA 02115 USA
| | - Robert J. Gorelick
- AIDS and Cancer Virus Program, Leidos Biomedical Research, Inc., Frederick National Laboratory for Cancer Research, Frederick, MD 21702-1201 USA
| | - Ioulia Rouzina
- Department of Chemistry and Biochemistry, Center for Retrovirus Research, and Center for RNA Biology, The Ohio State University, Columbus, OH 43210 USA
| | - Mark C. Williams
- Department of Physics, Northeastern University, Boston, MA 02115 USA
| | - Karin Musier-Forsyth
- Department of Chemistry and Biochemistry, Center for Retrovirus Research, and Center for RNA Biology, The Ohio State University, Columbus, OH 43210 USA
| | - Judith G. Levin
- Section on Viral Gene Regulation, Program in Genomics of Differentiation, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD 20892-2780 USA
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Abstract
RNAs are functionally diverse macromolecules whose proper functions rely strictly upon their correct tertiary structures. However, because of their high structural flexibility, correct folding of RNAs is challenging and slow. Therefore, cells and viruses encode a variety of RNA remodeling proteins, including helicases and RNA chaperones. In RNA viruses, these proteins are believed to play pivotal roles in all the processes involving viral RNAs during the life cycle. RNA helicases have been studied extensively for decades, whereas RNA chaperones, particularly virus-encoded RNA chaperones, are often overlooked. This review describes the activities of RNA chaperones encoded by RNA viruses, particularly the ones identified and characterized in recent years, and the functions of these proteins in different steps of viral life cycles, and presents an overview of this unique group of proteins.
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Affiliation(s)
- Jie Yang
- State Key Laboratory of Virology, College of Life Sciences, Wuhan University, Wuhan, 430072, China
| | - Hongjie Xia
- State Key Laboratory of Virology, College of Life Sciences, Wuhan University, Wuhan, 430072, China
| | - Qi Qian
- State Key Laboratory of Virology, College of Life Sciences, Wuhan University, Wuhan, 430072, China
| | - Xi Zhou
- State Key Laboratory of Virology, College of Life Sciences, Wuhan University, Wuhan, 430072, China.
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Wu T, Gorelick RJ, Levin JG. Selection of fully processed HIV-1 nucleocapsid protein is required for optimal nucleic acid chaperone activity in reverse transcription. Virus Res 2014; 193:52-64. [PMID: 24954787 PMCID: PMC4252486 DOI: 10.1016/j.virusres.2014.06.004] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/07/2014] [Revised: 06/09/2014] [Accepted: 06/10/2014] [Indexed: 12/14/2022]
Abstract
The mature HIV-1 nucleocapsid protein (NCp7) is generated by sequential proteolytic cleavage of precursor proteins containing additional C-terminal peptides: NCp15 (NCp7-spacer peptide 2 (SP2)-p6); and NCp9 (NCp7-SP2). Here, we compare the nucleic acid chaperone activities of the three proteins, using reconstituted systems that model the annealing and elongation steps in tRNA(Lys3)-primed (-) strong-stop DNA synthesis and subsequent minus-strand transfer. The maximum levels of annealing are similar for all of the proteins, but there are important differences in their ability to facilitate reverse transcriptase (RT)-catalyzed DNA extension. Thus, at low concentrations, NCp9 has the greatest activity, but with increasing concentrations, DNA synthesis is significantly reduced. This finding reflects NCp9's strong nucleic acid binding affinity (associated with the highly basic SP2 domain) as well as its slow dissociation kinetics, which together limit the ability of RT to traverse the nucleic acid template. NCp15 has the poorest activity of the three proteins due to its acidic p6 domain. Indeed, mutants with alanine substitutions for the acidic residues in p6 have improved chaperone function. Collectively, these data can be correlated with the known biological properties of NCp9 and NCp15 mutant virions and help to explain why mature NC has evolved as the critical cofactor for efficient virus replication and long-term viral fitness.
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Affiliation(s)
- Tiyun Wu
- Section on Viral Gene Regulation, Program in Genomics of Differentiation, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD 20892-2780, USA
| | - Robert J Gorelick
- AIDS and Cancer Virus Program, Leidos Biomedical Research, Inc., Frederick National Laboratory for Cancer Research, Frederick, MD 21702-1201, USA
| | - Judith G Levin
- Section on Viral Gene Regulation, Program in Genomics of Differentiation, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD 20892-2780, USA.
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Pachulska-Wieczorek K, Stefaniak AK, Purzycka KJ. Similarities and differences in the nucleic acid chaperone activity of HIV-2 and HIV-1 nucleocapsid proteins in vitro. Retrovirology 2014; 11:54. [PMID: 24992971 PMCID: PMC4227088 DOI: 10.1186/1742-4690-11-54] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/02/2014] [Accepted: 06/23/2014] [Indexed: 01/22/2023] Open
Abstract
Background The nucleocapsid domain of Gag and mature nucleocapsid protein (NC) act as nucleic acid chaperones and facilitate folding of nucleic acids at critical steps of retroviral replication cycle. The basic N-terminus of HIV-1 NC protein was shown most important for the chaperone activity. The HIV-2 NC (NCp8) and HIV-1 NC (NCp7) proteins possess two highly conserved zinc fingers, flanked by basic residues. However, the NCp8 N-terminal domain is significantly shorter and contains less positively charged residues. This study characterizes previously unknown, nucleic acid chaperone activity of the HIV-2 NC protein. Results We have comparatively investigated the in vitro nucleic acid chaperone properties of the HIV-2 and HIV-1 NC proteins. Using substrates derived from the HIV-1 and HIV-2 genomes, we determined the ability of both proteins to chaperone nucleic acid aggregation, annealing and strand exchange in duplex structures. Both NC proteins displayed comparable, high annealing activity of HIV-1 TAR DNA and its complementary nucleic acid. Interesting differences between the two NC proteins were discovered when longer HIV substrates, particularly those derived from the HIV-2 genome, were used in chaperone assays. In contrast to NCp7, NCp8 weakly facilitates annealing of HIV-2 TAR RNA to its complementary TAR (−) DNA. NCp8 is also unable to efficiently stimulate tRNALys3 annealing to its respective HIV-2 PBS motif. Using truncated NCp8 peptide, we demonstrated that despite the fact that the N-terminus of NCp8 differs from that of NCp7, this domain is essential for NCp8 activity. Conclusion Our data demonstrate that the HIV-2 NC protein displays reduced nucleic acid chaperone activity compared to that of HIV-1 NC. We found that NCp8 activity is limited by substrate length and stability to a greater degree than that of NCp7. This is especially interesting in light of the fact that the HIV-2 5′UTR is more structured than that of HIV-1. The reduced chaperone activity observed with NCp8 may influence the efficiency of reverse transcription and other key steps of the HIV-2 replication cycle.
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Mitra M, Wang W, Vo MN, Rouzina I, Barany G, Musier-Forsyth K. The N-terminal zinc finger and flanking basic domains represent the minimal region of the human immunodeficiency virus type-1 nucleocapsid protein for targeting chaperone function. Biochemistry 2013; 52:8226-36. [PMID: 24144434 DOI: 10.1021/bi401250a] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
The human immunodeficiency virus type-1 (HIV-1) nucleocapsid (NC) protein is a chaperone that facilitates nucleic acid conformational changes to produce the most thermodynamically stable arrangement. The critical role of NC in many steps of the viral life cycle makes it an attractive therapeutic target. The chaperone activity of NC depends on its nucleic acid aggregating ability, duplex destabilizing activity, and rapid on-off binding kinetics. During the minus-strand transfer step of reverse transcription, NC chaperones the annealing of highly structured transactivation response region (TAR) RNA to the complementary TAR DNA. In this work, the role of different functional domains of NC in facilitating 59-nucleotide TAR RNA-DNA annealing was probed by using chemically synthesized peptides derived from full-length (55 amino acids) HIV-1 NC: NC(1-14), NC(15-35), NC(1-28), NC(1-35), NC(29-55), NC(36-55), and NC(11-55). Most of these peptides displayed significantly reduced annealing kinetics, even when present at concentrations much higher than that of wild-type (WT) NC. In addition, these truncated NC constructs generally bind more weakly to single-stranded DNA and are less effective nucleic acid aggregating agents than full-length NC, consistent with the loss of both electrostatic and hydrophobic contacts. However, NC(1-35) displayed annealing kinetics, nucleic acid binding, and aggregation activity that were very similar to those of WT NC. Thus, we conclude that the N-terminal zinc finger, flanked by the N-terminus and linker domains, represents the minimal sequence that is necessary and sufficient for chaperone function in vitro. In addition, covalent continuity of the 35 N-terminal amino acids of NC is critical for full activity. Thus, although the hydrophobic pocket formed by residues proximal to the C-terminal zinc finger has been a major focus of recent anti-NC therapeutic strategies, NC(1-35) represents an alternative target for therapeutics aimed at disrupting NC's chaperone function.
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Affiliation(s)
- Mithun Mitra
- Department of Chemistry and Biochemistry, Center for RNA Biology, and Center for Retrovirus Research, The Ohio State University , Columbus, Ohio 43210, United States
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Mitra M, Hercík K, Byeon IJL, Ahn J, Hill S, Hinchee-Rodriguez K, Singer D, Byeon CH, Charlton LM, Nam G, Heidecker G, Gronenborn AM, Levin JG. Structural determinants of human APOBEC3A enzymatic and nucleic acid binding properties. Nucleic Acids Res 2013; 42:1095-110. [PMID: 24163103 PMCID: PMC3902935 DOI: 10.1093/nar/gkt945] [Citation(s) in RCA: 56] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Abstract
Human APOBEC3A (A3A) is a single-domain cytidine deaminase that converts deoxycytidine residues to deoxyuridine in single-stranded DNA (ssDNA). It inhibits a wide range of viruses and endogenous retroelements such as LINE-1, but it can also edit genomic DNA, which may play a role in carcinogenesis. Here, we extend our recent findings on the NMR structure of A3A and report structural, biochemical and cell-based mutagenesis studies to further characterize A3A’s deaminase and nucleic acid binding activities. We find that A3A binds ssRNA, but the RNA and DNA binding interfaces differ and no deamination of ssRNA is detected. Surprisingly, with only one exception (G105A), alanine substitution mutants with changes in residues affected by specific ssDNA binding retain deaminase activity. Furthermore, A3A binds and deaminates ssDNA in a length-dependent manner. Using catalytically active and inactive A3A mutants, we show that the determinants of A3A deaminase activity and anti-LINE-1 activity are not the same. Finally, we demonstrate A3A’s potential to mutate genomic DNA during transient strand separation and show that this process could be counteracted by ssDNA binding proteins. Taken together, our studies provide new insights into the molecular properties of A3A and its role in multiple cellular and antiviral functions.
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Affiliation(s)
- Mithun Mitra
- Section on Viral Gene Regulation, Program on Genomics of Differentiation, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD 20892-2780, USA, Department of Structural Biology, University of Pittsburgh School of Medicine, Pittsburgh, PA 15261, USA, Pittsburgh Center for HIV Protein Interactions, University of Pittsburgh School of Medicine, Pittsburgh, PA 15261, USA and HIV Drug Resistance Program, Frederick National Laboratory for Cancer Research, National Cancer Institute, Frederick, MD 21702, USA
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The nonstructural protein 2C of a Picorna-like virus displays nucleic acid helix destabilizing activity that can be functionally separated from its ATPase activity. J Virol 2013; 87:5205-18. [PMID: 23449794 DOI: 10.1128/jvi.00245-13] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
Abstract
Picorna-like viruses in the Picornavirales order are a large group of positive-strand RNA viruses that include numerous important pathogens for plants, insects, and humans. In these viruses, nonstructural protein 2C is one of the most conserved proteins and contains ATPase activity and putative RNA helicase activity. Here we expressed 2C protein of Ectropis obliqua picorna-like virus (EoV; genus Iflavirus, family Iflaviridae, order Picornavirales) in a eukaryotic expression system and determined that EoV 2C displays ATP-independent nucleic acid helix destabilizing and strand annealing acceleration activity in a concentration-dependent manner, indicating that this picornaviral 2C is more like an RNA chaperone than like the previously predicted RNA helicase. Our further characterization of EoV 2C revealed that divalent metal ions, such as Mg(2+) and Zn(2+), inhibit 2C-mediated helix destabilization to different extents. Moreover, we determined that EoV 2C also contains ATPase activity like that of other picornaviral 2C proteins and further assessed the functional relevance between its RNA chaperone-like and ATPase activities using mutational analysis as well as their responses to Mg(2+). Our data show that, when one of the two 2C activities was dramatically inhibited or almost abolished, the other activity could remain intact, showing that the RNA chaperone-like and ATPase activities of EoV 2C can be functionally separated. This report reveals that a picorna-like virus 2C protein displays RNA helix destabilizing and strand annealing acceleration activity, which may be critical for picornaviral replication and pathogenesis, and should foster our understanding of picorna-like viruses and viral RNA chaperones.
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9
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Hergott CB, Mitra M, Guo J, Wu T, Miller JT, Iwatani Y, Gorelick RJ, Levin JG. Zinc finger function of HIV-1 nucleocapsid protein is required for removal of 5'-terminal genomic RNA fragments: a paradigm for RNA removal reactions in HIV-1 reverse transcription. Virus Res 2013; 171:346-55. [PMID: 23149014 PMCID: PMC3578084 DOI: 10.1016/j.virusres.2012.08.013] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/10/2012] [Revised: 07/27/2012] [Accepted: 08/20/2012] [Indexed: 11/28/2022]
Abstract
During (-) strong-stop DNA [(-) SSDNA] synthesis, RNase H cleavage of genomic viral RNA generates small 5'-terminal RNA fragments (14-18 nt) that remain annealed to the DNA. Unless these fragments are removed, the minus-strand transfer reaction, required for (-) SSDNA elongation, cannot occur. Here, we describe the mechanism of 5'-terminal RNA removal and the roles of HIV-1 nucleocapsid protein (NC) and RNase H cleavage in this process. Using an NC-dependent system that models minus-strand transfer, we show that the presence of short terminal fragments pre-annealed to (-) SSDNA has no impact on strand transfer, implying efficient fragment removal. Moreover, in reactions with an RNase H(-) reverse transcriptase mutant, NC alone is able to facilitate fragment removal, albeit less efficiently than in the presence of both RNase H activity and NC. Results obtained from novel electrophoretic gel mobility shift and Förster Resonance Energy Transfer assays, which each directly measure RNA fragment release from a duplex in the absence of DNA synthesis, demonstrate for the first time that the architectural integrity of NC's zinc finger (ZF) domains is absolutely required for this reaction. This suggests that NC's helix destabilizing activity (associated with the ZFs) facilitates strand exchange through the displacement of these short terminal RNAs by the longer 3' acceptor RNA, which forms a more stable duplex with (-) SSDNA. Taken together with previously published results, we conclude that NC-mediated fragment removal is linked mechanistically with selection of the correct primer for plus-strand DNA synthesis and tRNA removal step prior to plus-strand transfer. Thus, HIV-1 has evolved a single mechanism for these RNA removal reactions that are critical for successful reverse transcription.
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MESH Headings
- DNA, Viral/chemistry
- DNA, Viral/genetics
- DNA, Viral/metabolism
- Gene Expression Regulation, Viral
- HIV-1/chemistry
- HIV-1/genetics
- HIV-1/metabolism
- RNA Processing, Post-Transcriptional
- RNA, Viral/chemistry
- RNA, Viral/genetics
- RNA, Viral/metabolism
- Reverse Transcription
- Zinc Fingers
- gag Gene Products, Human Immunodeficiency Virus/chemistry
- gag Gene Products, Human Immunodeficiency Virus/genetics
- gag Gene Products, Human Immunodeficiency Virus/metabolism
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Affiliation(s)
- Christopher B. Hergott
- Section on Viral Gene Regulation, Program on Genomics of Differentiation, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD 20892-2780, USA
| | - Mithun Mitra
- Section on Viral Gene Regulation, Program on Genomics of Differentiation, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD 20892-2780, USA
| | - Jianhui Guo
- Section on Viral Gene Regulation, Program on Genomics of Differentiation, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD 20892-2780, USA
| | - Tiyun Wu
- Section on Viral Gene Regulation, Program on Genomics of Differentiation, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD 20892-2780, USA
| | - Jennifer T. Miller
- Reverse Transcriptase Biochemistry Section, HIV Drug Resistance Program, National Cancer Institute, National Institutes of Health, Frederick National Laboratory for Cancer Research, Frederick, MD 21702-1201, USA
| | - Yasumasa Iwatani
- Section on Viral Gene Regulation, Program on Genomics of Differentiation, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD 20892-2780, USA
| | - Robert J. Gorelick
- AIDS and Cancer Virus Program, SAIC-Frederick, Inc., Frederick National Laboratory for Cancer Research, Frederick, MD 21702-1201, USA
| | - Judith G. Levin
- Section on Viral Gene Regulation, Program on Genomics of Differentiation, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD 20892-2780, USA
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10
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Godet J, Boudier C, Humbert N, Ivanyi-Nagy R, Darlix JL, Mély Y. Comparative nucleic acid chaperone properties of the nucleocapsid protein NCp7 and Tat protein of HIV-1. Virus Res 2012; 169:349-60. [PMID: 22743066 PMCID: PMC7114403 DOI: 10.1016/j.virusres.2012.06.021] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/30/2012] [Revised: 06/18/2012] [Accepted: 06/19/2012] [Indexed: 10/28/2022]
Abstract
RNA chaperones are proteins able to rearrange nucleic acid structures towards their most stable conformations. In retroviruses, the reverse transcription of the viral RNA requires multiple and complex nucleic acid rearrangements that need to be chaperoned. HIV-1 has evolved different viral-encoded proteins with chaperone activity, notably Tat and the well described nucleocapsid protein NCp7. We propose here an overview of the recent reports that examine and compare the nucleic acid chaperone properties of Tat and NCp7 during reverse transcription to illustrate the variety of mechanisms of action of the nucleic acid chaperone proteins.
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Affiliation(s)
- Julien Godet
- Laboratoire de Biophotonique et Pharmacologie, Faculté de Pharmacie, UMR 7213 CNRS, Université de Strasbourg, 67401 Illkirch, France
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11
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Thomas JA, Shatzer TL, Gorelick RJ. Blocking premature reverse transcription fails to rescue the HIV-1 nucleocapsid-mutant replication defect. Retrovirology 2011; 8:46. [PMID: 21682883 PMCID: PMC3141651 DOI: 10.1186/1742-4690-8-46] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/01/2011] [Accepted: 06/17/2011] [Indexed: 02/06/2023] Open
Abstract
Background The nucleocapsid (NC) protein of HIV-1 is critical for viral replication. Mutational analyses have demonstrated its involvement in viral assembly, genome packaging, budding, maturation, reverse transcription, and integration. We previously reported that two conservative NC mutations, His23Cys and His44Cys, cause premature reverse transcription such that mutant virions contain approximately 1,000-fold more DNA than wild-type virus, and are replication defective. In addition, both mutants show a specific defect in integration after infection. Results In the present study we investigated whether blocking premature reverse transcription would relieve the infectivity defects, which we successfully performed by transfecting proviral plasmids into cells cultured in the presence of high levels of reverse transcriptase inhibitors. After subsequent removal of the inhibitors, the resulting viruses showed no significant difference in single-round infective titer compared to viruses where premature reverse transcription did occur; there was no rescue of the infectivity defects in the NC mutants upon reverse transcriptase inhibitor treatment. Surprisingly, time-course endogenous reverse transcription assays demonstrated that the kinetics for both the NC mutants were essentially identical to wild-type when premature reverse transcription was blocked. In contrast, after infection of CD4+ HeLa cells, it was observed that while the prevention of premature reverse transcription in the NC mutants resulted in lower quantities of initial reverse transcripts, the kinetics of reverse transcription were not restored to that of untreated wild-type HIV-1. Conclusions Premature reverse transcription is not the cause of the replication defect but is an independent side-effect of the NC mutations.
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Affiliation(s)
- James A Thomas
- AIDS and Cancer Virus Program, SAIC-Frederick, Inc,, NCI at Frederick, Frederick, MD 21702, USA
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12
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Levin JG, Mitra M, Mascarenhas A, Musier-Forsyth K. Role of HIV-1 nucleocapsid protein in HIV-1 reverse transcription. RNA Biol 2010; 7:754-74. [PMID: 21160280 DOI: 10.4161/rna.7.6.14115] [Citation(s) in RCA: 130] [Impact Index Per Article: 9.3] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022] Open
Abstract
The HIV-1 nucleocapsid protein (NC) is a nucleic acid chaperone, which remodels nucleic acid structures so that the most thermodynamically stable conformations are formed. This activity is essential for virus replication and has a critical role in mediating highly specific and efficient reverse transcription. NC's function in this process depends upon three properties: (1) ability to aggregate nucleic acids; (2) moderate duplex destabilization activity; and (3) rapid on-off binding kinetics. Here, we present a detailed molecular analysis of the individual events that occur during viral DNA synthesis and show how NC's properties are important for almost every step in the pathway. Finally, we also review biological aspects of reverse transcription during infection and the interplay between NC, reverse transcriptase, and human APOBEC3G, an HIV-1 restriction factor that inhibits reverse transcription and virus replication in the absence of the HIV-1 Vif protein.
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Affiliation(s)
- Judith G Levin
- Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD, USA.
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13
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Wu T, Datta SA, Mitra M, Gorelick RJ, Rein A, Levin JG. Fundamental differences between the nucleic acid chaperone activities of HIV-1 nucleocapsid protein and Gag or Gag-derived proteins: biological implications. Virology 2010; 405:556-67. [PMID: 20655566 PMCID: PMC2963451 DOI: 10.1016/j.virol.2010.06.042] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/27/2010] [Revised: 05/16/2010] [Accepted: 06/23/2010] [Indexed: 01/31/2023]
Abstract
The HIV-1 Gag polyprotein precursor has multiple domains including nucleocapsid (NC). Although mature NC and NC embedded in Gag are nucleic acid chaperones (proteins that remodel nucleic acid structure), few studies include detailed analysis of the chaperone activity of partially processed Gag proteins and comparison with NC and Gag. Here we address this issue by using a reconstituted minus-strand transfer system. NC and NC-containing Gag proteins exhibited annealing and duplex destabilizing activities required for strand transfer. Surprisingly, unlike NC, with increasing concentrations, Gag proteins drastically inhibited the DNA elongation step. This result is consistent with "nucleic acid-driven multimerization" of Gag and the reported slow dissociation of Gag from bound nucleic acid, which prevent reverse transcriptase from traversing the template ("roadblock" mechanism). Our findings illustrate one reason why NC (and not Gag) has evolved as a critical cofactor in reverse transcription, a paradigm that might also extend to other retrovirus systems.
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Affiliation(s)
- Tiyun Wu
- Laboratory of Molecular Genetics, Program in Genomics of Differentiation, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Building 6B, Room 216, 6 Center Drive, Bethesda, MD 20892-2780, USA
| | - Siddhartha A.K. Datta
- HIV Drug Resistance Program, National Cancer Institute-Frederick, Frederick, MD 21702-1201, USA
| | - Mithun Mitra
- Laboratory of Molecular Genetics, Program in Genomics of Differentiation, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Building 6B, Room 216, 6 Center Drive, Bethesda, MD 20892-2780, USA
| | - Robert J. Gorelick
- AIDS and Cancer Virus Program, SAIC-Frederick, Inc., National Cancer Institute-Frederick, Frederick, MD 21702-1201, USA
| | - Alan Rein
- HIV Drug Resistance Program, National Cancer Institute-Frederick, Frederick, MD 21702-1201, USA
| | - Judith G. Levin
- Laboratory of Molecular Genetics, Program in Genomics of Differentiation, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Building 6B, Room 216, 6 Center Drive, Bethesda, MD 20892-2780, USA
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14
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Post K, Kankia B, Gopalakrishnan S, Yang V, Cramer E, Saladores P, Gorelick RJ, Guo J, Musier-Forsyth K, Levin JG. Fidelity of plus-strand priming requires the nucleic acid chaperone activity of HIV-1 nucleocapsid protein. Nucleic Acids Res 2009; 37:1755-66. [PMID: 19158189 PMCID: PMC2665208 DOI: 10.1093/nar/gkn1045] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
During minus-strand DNA synthesis, RNase H degrades viral RNA sequences, generating potential plus-strand DNA primers. However, selection of the 3' polypurine tract (PPT) as the exclusive primer is required for formation of viral DNA with the correct 5'-end and for subsequent integration. Here we show a new function for the nucleic acid chaperone activity of HIV-1 nucleocapsid protein (NC) in reverse transcription: blocking mispriming by non-PPT RNAs. Three representative 20-nt RNAs from the PPT region were tested for primer extension. Each primer had activity in the absence of NC, but less than the PPT. NC reduced priming by these RNAs to essentially base-line level, whereas PPT priming was unaffected. RNase H cleavage and zinc coordination by NC were required for maximal inhibition of mispriming. Biophysical properties, including thermal stability, helical structure and reverse transcriptase (RT) binding affinity, showed significant differences between PPT and non-PPT duplexes and the trends were generally correlated with the biochemical data. Binding studies in reactions with both NC and RT ruled out a competition binding model to explain NC's observed effects on mispriming efficiency. Taken together, these results demonstrate that NC chaperone activity has a major role in ensuring the fidelity of plus-strand priming.
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Affiliation(s)
- Klara Post
- Laboratory of Molecular Genetics, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD 20892, USA
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15
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Vo MN, Barany G, Rouzina I, Musier-Forsyth K. Effect of Mg(2+) and Na(+) on the nucleic acid chaperone activity of HIV-1 nucleocapsid protein: implications for reverse transcription. J Mol Biol 2009; 386:773-88. [PMID: 19154740 DOI: 10.1016/j.jmb.2008.12.073] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/30/2008] [Revised: 12/20/2008] [Accepted: 12/29/2008] [Indexed: 11/18/2022]
Abstract
The human immunodeficiency virus type 1 (HIV-1) nucleocapsid protein (NC) is an essential protein for retroviral replication. Among its numerous functions, NC is a nucleic acid (NA) chaperone protein that catalyzes NA rearrangements leading to the formation of thermodynamically more stable conformations. In vitro, NC chaperone activity is typically assayed under conditions of low or no Mg(2+), even though reverse transcription requires the presence of divalent cations. Here, the chaperone activity of HIV-1 NC was studied as a function of varying Na(+) and Mg(2+) concentrations by investigating the annealing of complementary DNA and RNA hairpins derived from the trans-activation response domain of the HIV genome. This reaction mimics the annealing step of the minus-strand transfer process in reverse transcription. Gel-shift annealing and sedimentation assays were used to monitor the annealing kinetics and aggregation activity of NC, respectively. In the absence of protein, a limited ability of Na(+) and Mg(2+) cations to facilitate hairpin annealing was observed, whereas NC stimulated the annealing 10(3)- to 10(5)-fold. The major effect of either NC or the cations is on the rate of bimolecular association of the hairpins. This effect is especially strong under conditions wherein NC induces NA aggregation. Titration with NC and NC/Mg(2+) competition studies showed that the annealing kinetics depends only on the level of NA saturation with NC. NC competes with Mg(2+) or Na(+) for sequence-nonspecific NA binding similar to a simple trivalent cation. Upon saturation, NC induces attraction between NA molecules corresponding to approximately 0.3 kcal/mol/nucleotide, in agreement with an electrostatic mechanism of NC-induced NA aggregation. These data provide insights into the variable effects of NC's chaperone activity observed during in vitro studies of divalent metal-dependent reverse transcription reactions and suggest the feasibility of NC-facilitated proviral DNA synthesis within the mature capsid core.
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Affiliation(s)
- My-Nuong Vo
- Department of Chemistry and Institute for Molecular Virology, University of Minnesota, Minneapolis, MN 55455, USA
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16
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Grohmann D, Godet J, Mély Y, Darlix JL, Restle T. HIV-1 nucleocapsid traps reverse transcriptase on nucleic acid substrates. Biochemistry 2008; 47:12230-40. [PMID: 18947237 DOI: 10.1021/bi801386r] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Conversion of the genomic RNA of human immunodeficiency virus (HIV) into full-length viral DNA is a complex multistep reaction catalyzed by the reverse transcriptase (RT). Numerous studies have shown that the viral nucleocapsid (NC) protein has a vital impact on various steps during reverse transcription, which is crucial for virus infection. However, the exact molecular details are poorly defined. Here, we analyzed the effect of NC on RT-catalyzed single-turnover, single-nucleotide incorporation using different nucleic acid substrates. In the presence of NC, we observed an increase in the amplitude of primer extension of up to 3-fold, whereas the transient rate of nucleotide incorporation ( k pol) dropped by up to 50-fold. To unravel the underlying molecular mechanism, we carefully analyzed the effect of NC on RT-nucleic acid substrate dissociation. The studies revealed that NC considerably enhances the stability of RT-substrate complexes by reducing the observed dissociation rate constants, which more than compensates for the observed drop in k pol. In conclusion, our data strongly support the concept that NC not only indirectly assists the reverse transcription process by its nucleic acid chaperoning activity but also positively affects the RT-catalyzed nucleotide incorporation reaction by increasing polymerase processivity presumably via a physical interaction of the two viral proteins.
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Affiliation(s)
- Dina Grohmann
- Institut Gilbert Laustriat, Photophysique des interactions moleculaires, UMR 7175 CNRS, Faculte de Pharmacie, Universite Louis Pasteur, Strasbourg 1, 74, Route du Rhin, 67401 Illkirch, France
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17
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Zúñiga S, Sola I, Cruz JLG, Enjuanes L. Role of RNA chaperones in virus replication. Virus Res 2008; 139:253-66. [PMID: 18675859 PMCID: PMC7114511 DOI: 10.1016/j.virusres.2008.06.015] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/03/2008] [Revised: 06/18/2008] [Accepted: 06/23/2008] [Indexed: 01/06/2023]
Abstract
RNA molecules are functionally diverse in part due to their extreme structural flexibility that allows rapid regulation by refolding. RNA folding could be a difficult process as often molecules adopt a spatial conformation that is very stable but not biologically functional, named a kinetic trap. RNA chaperones are non-specific RNA binding proteins that help RNA folding by resolving misfolded structures or preventing their formation. There is a large number of viruses whose genome is RNA that allows some evolutionary advantages, such as rapid genome mutation. On the other hand, regions of the viral RNA genomes can adopt different structural conformations, some of them lacking functional relevance and acting as misfolded intermediates. In fact, for an efficient replication, they often require RNA chaperone activities. There is a growing list of RNA chaperones encoded by viruses involved in different steps of the viral cycle. Also, cellular RNA chaperones have been involved in replication of RNA viruses. This review briefly describes RNA chaperone activities and is focused in the roles that viral or cellular nucleic acid chaperones have in RNA virus replication, particularly in those viruses that require discontinuous RNA synthesis.
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Affiliation(s)
- Sonia Zúñiga
- Centro Nacional de Biotecnología, CSIC, Department of Molecular and Cell Biology, Campus Universitario de Cantoblanco, Darwin 3, 28049 Madrid, Spain
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18
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Jacob DT, DeStefano JJ. A new role for HIV nucleocapsid protein in modulating the specificity of plus strand priming. Virology 2008; 378:385-96. [PMID: 18632127 DOI: 10.1016/j.virol.2008.06.002] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/05/2008] [Revised: 05/26/2008] [Accepted: 06/05/2008] [Indexed: 11/28/2022]
Abstract
The current study indicates a new role for HIV nucleocapsid protein (NC) in modulating the specificity of plus strand priming. RNase H cleavage by reverse transcriptase (RT) during minus strand synthesis gives rise to RNA fragments that could potentially be used as primers for synthesis of the plus strand, leading to the initiation of priming from multiple points as has been observed for other retroviruses. For HIV, the central and 3' polypurine tracts (PPTs) are the major sites of plus strand initiation. Using reconstituted in vitro assays, results showed that NC greatly reduced the efficiency of extension of non-PPT RNA primers, but not PPT. Experiments mimicking HIV replication showed that RT generated and used both PPT and non-PPT RNAs to initiate "plus strand" synthesis, but non-PPT usage was strongly inhibited by NC. The results support a role for NC in specifying primer usage during plus strand synthesis.
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Affiliation(s)
- Deena T Jacob
- Department of Cell Biology and Molecular Genetics, University of Maryland, College Park, Maryland 20742, USA
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19
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Nucleocapsid protein function in early infection processes. Virus Res 2008; 134:39-63. [PMID: 18279991 DOI: 10.1016/j.virusres.2007.12.006] [Citation(s) in RCA: 124] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/10/2007] [Revised: 12/13/2007] [Accepted: 12/13/2007] [Indexed: 01/15/2023]
Abstract
The role of nucleocapsid protein (NC) in the early steps of retroviral replication appears largely that of a facilitator for reverse transcription and integration. Using a wide variety of cell-free assay systems, the properties of mature NC proteins (e.g. HIV-1 p7(NC) or MLV p10(NC)) as nucleic acid chaperones have been extensively investigated. The effect of NC on tRNA annealing, reverse transcription initiation, minus-strand-transfer, processivity of reverse transcription, plus-strand-transfer, strand-displacement synthesis, 3' processing of viral DNA by integrase, and integrase-mediated strand-transfer has been determined by a large number of laboratories. Interestingly, these reactions can all be accomplished to varying degrees in the absence of NC; some are facilitated by both viral and non-viral proteins and peptides that may or may not be involved in vivo. What is one to conclude from the observation that NC is not strictly required for these necessary reactions to occur? NC likely enhances the efficiency of each of these steps, thereby vastly improving the productivity of infection. In other words, one of the major roles of NC is to enhance the effectiveness of early infection, thereby increasing the probability of productive replication and ultimately of retrovirus survival.
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20
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Strand transfer events during HIV-1 reverse transcription. Virus Res 2008; 134:19-38. [PMID: 18279992 DOI: 10.1016/j.virusres.2007.12.017] [Citation(s) in RCA: 96] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/27/2007] [Revised: 12/19/2007] [Accepted: 12/20/2007] [Indexed: 11/20/2022]
Abstract
Human immunodeficiency virus type 1 (HIV-1) and other retroviruses replicate through reverse transcription, a process in which the single stranded RNA of the viral genome is converted to a double stranded DNA. The virally encoded reverse transcriptase (RT) mediates reverse transcription through DNA polymerase and RNase H activities. Conversion of the plus strand RNA to plus/minus strand RNA/DNA hybrid involves a transfer of the growing DNA strand from one site on the genomic RNA to another. This is called minus strong-stop DNA transfer. Later synthesis of the second or plus DNA strand involves a second strand transfer, involving a similar mechanism as the minus strand transfer. A basic feature of the strand transfer mechanism is the use of the RT RNase H to remove segments of the RNA template strand from the growing DNA strand, freeing a single stranded region to anneal to the second site. Viral nucleocapsid protein (NC) functions to promote transfer by facilitating this strand exchange process. Two copies of the RNA genomes, sometimes non-identical, are co-packaged in the genomes of retroviruses. The properties of the reverse transcriptase allow a transfer of the growing DNA strand between these genomes to occur occasionally at any point during reverse transcription, producing recombinant viral progeny. Recombination promotes structural diversity of the virus that helps it to survive host immunity and drug therapy. Recombination strand transfer can be forced by a break in the template, or can occur at sites where folding structure of the template pauses the RT, allowing a concentration of RNase H cleavages that promote transfers. Transfer can be a simple one-step process, or can proceed by a complex multi-step invasion mechanism. In this latter process, the second RNA template interacts with the growing DNA strand well behind the DNA 3'-terminus. The newly formed RNA-DNA hybrid expands by branch migration and eventually catches the elongating DNA primer 3'-terminus to complete the transfer. Transfers are also promoted by interactions between the two RNA templates, which accelerate transfer by a proximity effect. Other details of the role of strand transfers in reverse transcription and the biochemical features of the transfer reaction are discussed.
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21
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Song M, Basu VP, Hanson MN, Roques BP, Bambara RA. Proximity and branch migration mechanisms in HIV-1 minus strand strong stop DNA transfer. J Biol Chem 2007; 283:3141-3150. [PMID: 18073206 DOI: 10.1074/jbc.m707343200] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Human immunodeficiency virus type 1 minus strand transfer was measured using a genomic donor-acceptor template system in vitro. Donor RNA D199, having the minimum region required for minus strong stop DNA synthesis, was previously shown to transfer with 35% efficiency to an acceptor RNA representing the 3' repeat region. Donor D520, having an additional 321-nucleotide segment extending into gag, transferred at 75% efficiency. In this study each transfer step was analyzed to account for the difference. Measurement of terminal transfer indicated that the 3' terminus of the cDNA generated using D520 is more accessible for transfer than that of D199. Nevertheless, acceptor competition experiments demonstrated that D520 has a greater preference for invasion-driven versus terminal transfer than D199. Competition mapping showed that the base of the transactivation response element is the primary invasion site for D520, important for efficient acceptor invasion. Acceptors complementary to the invasion and terminal transfer sites, but not the region between, allowed assessment of the significance of hybrid propagation by branch migration. These bipartite acceptors showed that with D520, invasion raises the local concentration of the acceptor for efficient terminal transfer by a proximity effect. However, with D199, invasion is relatively inefficient, and the cDNA 3' terminus is not very accessible. For most transfers that occurred, the acceptor accessed the cDNA 3' end by branch migration. Results suggest that both proximity and branch migration mechanisms contribute to transfers, with the proportion determined by donor-cDNA structure. D520 transfers better because it has greater accessibility for both invasion and terminus transfer.
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Affiliation(s)
- Min Song
- Department of Biochemistry and Biophysics, University of Rochester, Rochester, New York 14642
| | - Vandana P Basu
- Department of Biochemistry and Biophysics, University of Rochester, Rochester, New York 14642
| | - Mark N Hanson
- Department of Biochemistry and Biophysics, University of Rochester, Rochester, New York 14642
| | - Bernard P Roques
- Departement de Pharmacochimie Moleculaire et Structurale, INSERM U266, CNRS UMR 8600, Faculte de Pharmacie, 4, Avenue De l'Observatoire, 75270 Paris Cedex 06, France
| | - Robert A Bambara
- Department of Biochemistry and Biophysics, University of Rochester, Rochester, New York 14642.
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22
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Ramalanjaona N, de Rocquigny H, Millet A, Ficheux D, Darlix JL, Mély Y. Investigating the mechanism of the nucleocapsid protein chaperoning of the second strand transfer during HIV-1 DNA synthesis. J Mol Biol 2007; 374:1041-53. [PMID: 18028945 DOI: 10.1016/j.jmb.2007.10.001] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/21/2007] [Revised: 09/26/2007] [Accepted: 10/01/2007] [Indexed: 10/22/2022]
Abstract
Conversion of the human immunodeficiency virus type 1 (HIV-1) genomic RNA into the proviral DNA by reverse transcriptase involves two obligatory strand transfers that are chaperoned by the nucleocapsid protein (NC). The second strand transfer relies on the annealing of the (-) and (+) copies of the primer binding site, (-)PBS and (+) PBS, which fold into complementary stem-loops (SLs) with terminal single-stranded overhangs. To understand how NC chaperones their hybridization, we investigated the annealing kinetics of fluorescently labelled (+)PBS with various (-)PBS derivatives. In the absence of NC, the (+)/(-)PBS annealing was governed by a second-order pathway nucleated mainly by the single-stranded overhangs of the two PBS SLs. The annealing reaction appeared to be rate-limited by the melting of the stable G.C-rich stem subsequent to the formation of the partially annealed intermediate. A second pathway nucleated through the loops could be detected, but was very minor. NC(11-55), which consists primarily of the zinc finger domain, increased the (-)/(+) PBS annealing kinetics by about sixfold, by strongly activating the interaction between the PBS loops. NC(11-55) also activated (-)/(+) PBS annealing through the single-strand overhangs, but by a factor of only 2. Full-length NC(1-55) further increased the (-)/(+)PBS annealing kinetics by tenfold. The NC-promoted (-)/(+)PBS mechanism proved to be similar with extended (-)DNA molecules, suggesting that it is relevant in the context of proviral DNA synthesis. These findings favour the notion that the ubiquitous role of NC in the viral life-cycle probably relies on the ability of NC to chaperone nucleic acid hybridization via different mechanisms.
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Affiliation(s)
- Nick Ramalanjaona
- Photophysique des interactions biomoléculaires, UMR 7175 CNRS, Institut Gilbert Laustriat, Faculté de Pharmacie, Université Louis Pasteur, Strasbourg 1, 74, Route du Rhin, 67401 ILLKIRCH Cedex, France
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