Initiation of HIV-1 Reverse Transcription Is Regulated by a Primer Activation Signal

Abstract

Reverse transcription of the human immunodeficiency virus type 1 (HIV-1) RNA genome appears to be strictly regulated at the level of initiation. The primer binding site (PBS), at which the tRNA 3Lys molecule anneals and reverse transcription is initiated, is present in a highly structured region of the untranslated leader RNA. Detailed mutational analysis of the U5 leader stem identified a sequence motif in the U5 region that is critical for activation of the PBS-bound tRNA 3Lys primer. This U5 motif, termed the primer activation signal ( PAS ), may interact with the TΨC arm of the tRNA 3Lys primer, similar to the additional interaction proposed for the genome of Rous sarcoma virus and its tRNATrp primer. This suggests that reverse transcription is regulated by a common mechanism in all retroviruses. In HIV-1 , the PAS is masked through base pairing in the U5 leader stem. This provides a mechanism for positive and negative regulation of reverse transcription. Based on structure probing of the mutant and wild-type RNAs, an RNA secondary structure model is proposed that juxtaposes the critical PAS and PBS motifs. Reverse transcription of the human immunodeficiency virus type 1 (HIV-1) RNA genome appears to be strictly regulated at the level of initiation. The primer binding site (PBS), at which the tRNA 3Lys molecule anneals and reverse transcription is initiated, is present in a highly structured region of the untranslated leader RNA. Detailed mutational analysis of the U5 leader stem identified a sequence motif in the U5 region that is critical for activation of the PBS-bound tRNA 3Lys primer. This U5 motif, termed the primer activation signal ( PAS ), may interact with the TΨC arm of the tRNA 3Lys primer, similar to the additional interaction proposed for the genome of Rous sarcoma virus and its tRNATrp primer. This suggests that reverse transcription is regulated by a common mechanism in all retroviruses. In HIV-1 , the PAS is masked through base pairing in the U5 leader stem. This provides a mechanism for positive and negative regulation of reverse transcription. Based on structure probing of the mutant and wild-type RNAs, an RNA secondary structure model is proposed that juxtaposes the critical PAS and PBS motifs. reverse transcriptase primer binding site human immunodeficiency virus type 1 Rous sarcoma virus viral RNA primer activation signal long terminal repeat polymerase chain reaction diethyl pyrocarbonate dimethyl sulfate nucleocapsid nucleotide(s) Infection of the host cell by a retroviral particle results in reverse transcription of the viral RNA genome into double-stranded DNA, which subsequently becomes integrated into the host cell genome (1Telesnitsky A. Goff S.P. Retroviruses. Cold Spring Harbor Laboratory, Cold Spring Harbor, NY1997: 121-160Google Scholar). Reverse transcription is mediated by the virion-associated enzyme reverse transcriptase (RT),1and a cellular tRNA molecule is used as a primer (2Marquet R. Isel C. Ehresmann C. Ehresmann B. Biochimie (Paris). 1995; 77: 113-124Crossref PubMed Scopus (200) Google Scholar). The tRNA primer binds with its 3′-terminal 18 nts to a complementary sequence, the primer binding site (PBS), that is located in the 5′-untranslated leader region of the viral RNA genome. Retroviral particles are competent to initiate reverse transcription shortly after budding from the producer cell, but there is also evidence that reverse transcription in virions is limited (3Trono D. J. Virol. 1992; 66: 4893-4900Crossref PubMed Google Scholar, 4Lori F. Veronese F.D.M. De Vico A.L. Lusso P. Reitz Jr., M.S. Gallo R.C. J. Virol. 1992; 66: 5067-5074Crossref PubMed Google Scholar, 5Arts E.J. Mak J. Kleiman L. Wainberg M.A. J. Gen. Virol. 1994; 75: 1605-1613Crossref PubMed Scopus (35) Google Scholar, 6Oude Essink B.B. Das A.T. Berkhout B. J. Mol. Biol. 1996; 264: 243-254Crossref PubMed Scopus (41) Google Scholar, 7Huang Y. Wang J. Shalom A. Li Z. Khorchid A. Wainberg M.A. Kleiman L. J. Virol. 1997; 71: 726-728Crossref PubMed Google Scholar). This suggests that initiation of reverse transcription is restricted until a new host cell is infected. The mechanism that regulates reverse transcription is not known, but sequence motifs and RNA secondary structures in the region flanking the PBS have been implicated (8Cobrinik D. Soskey L. Leis J. J. Virol. 1988; 62: 3622-3630Crossref PubMed Google Scholar, 9Cobrinik D. Aiyar A. Ge Z. Katzman M. Huang H. Leis J. J. Virol. 1991; 65: 3864-3872Crossref PubMed Google Scholar, 10Cordell B. Swanstrom R. Goodman H.M. Bishop J.M. J. Biol. Chem. 1979; 254: 1866-1874Abstract Full Text PDF PubMed Google Scholar, 11Beerens N. Klaver B. Berkhout B. J. Virol. 2000; 74: 2227-2238Crossref PubMed Scopus (25) Google Scholar, 12Isel C. Ehresmann C. Keith G. Ehresmann B. Marquet R. J. Mol. Biol. 1995; 247: 236-250Crossref PubMed Scopus (229) Google Scholar, 13Liang C. Li X. Rong L. Inouye P. Quan Y. Kleiman L. Wainberg M.A. J. Virol. 1997; 71: 5750-5757Crossref PubMed Google Scholar). Alternatively, reverse transcription may be restricted in extracellular virions by the low concentration of dNTP molecules in virus particles. In the genome of human immunodeficiency virus type I (HIV-1), the PBS is predicted to be part of an extended RNA structure. Several RNA secondary structure models have been proposed for this region of the 5′-untranslated leader (14Berkhout B. Progr. Nucleic Acid. Res. Mol. Biol. 1996; 54: 1-34Crossref PubMed Google Scholar, 15Baudin F. Marquet R. Isel C. Darlix J.L. Ehresmann B. Ehresmann C. J. Mol. Biol. 1993; 229: 382-397Crossref PubMed Scopus (276) Google Scholar, 16Rizvi T.A. Panganiban A.T. J. Virol. 1993; 67: 2681-2688Crossref PubMed Google Scholar, 17Damgaard C.K. Dyhr-Mikkelsen H. Kjems J. Nucleic Acids Res. 1998; 26: 3667-3676Crossref PubMed Scopus (90) Google Scholar), and there is recent evidence that this region can adopt alternate conformations (18Berkhout B. vanWamel J.L.B. RNA (N. Y.). 2000; 6: 282-295Crossref PubMed Scopus (84) Google Scholar, 19Huthoff H.T. Berkhout B. RNA (N. Y.). 2001; 7: 143-157Crossref PubMed Scopus (180) Google Scholar). The model depicted in Fig. 1 A shows the U5-PBS hairpin that occludes part of the PBS and the extended U5 leader stem, which is formed by base pairing of sequences in the upstream U5 and the downstream leader region. Similar RNA secondary structures have been predicted for other retroviruses (16Rizvi T.A. Panganiban A.T. J. Virol. 1993; 67: 2681-2688Crossref PubMed Google Scholar, 20Berkhout B. Schoneveld I. Nucleic Acids Res. 1993; 21: 1171-1178Crossref PubMed Scopus (58) Google Scholar, 21Morris S. Leis J. J. Virol. 1999; 73: 6307-6318Crossref PubMed Google Scholar, 22Aiyar A. Cobrinik D. Ge Z. Kung H.J. Leis J. J. Virol. 1992; 66: 2464-2472Crossref PubMed Google Scholar, 23Berkhout B. Nucleic Acids Res. 1997; 25: 4013-4017Crossref PubMed Scopus (24) Google Scholar). For the avian Rous sarcoma virus (RSV), these structures have been reported to regulate initiation of reverse transcription (8Cobrinik D. Soskey L. Leis J. J. Virol. 1988; 62: 3622-3630Crossref PubMed Google Scholar, 9Cobrinik D. Aiyar A. Ge Z. Katzman M. Huang H. Leis J. J. Virol. 1991; 65: 3864-3872Crossref PubMed Google Scholar, 10Cordell B. Swanstrom R. Goodman H.M. Bishop J.M. J. Biol. Chem. 1979; 254: 1866-1874Abstract Full Text PDF PubMed Google Scholar, 24Miller J.T. Ge Z. Morris S. Das K. Leis J. J. Virol. 1997; 71: 7648-7656Crossref PubMed Google Scholar). In RSV, reverse transcription is stimulated by an additional vRNA-tRNA interaction between a sequence motif in the U5 region and the TΨC arm of the tRNATrp primer (22Aiyar A. Cobrinik D. Ge Z. Kung H.J. Leis J. J. Virol. 1992; 66: 2464-2472Crossref PubMed Google Scholar). For HIV-1 reverse transcription, initiation is thought to be stimulated by other template-primer contacts, including a base-pairing interaction between the A-rich loop of the U5-PBS hairpin and the anti-codon loop of the tRNA 3Lys primer (12Isel C. Ehresmann C. Keith G. Ehresmann B. Marquet R. J. Mol. Biol. 1995; 247: 236-250Crossref PubMed Scopus (229) Google Scholar, 13Liang C. Li X. Rong L. Inouye P. Quan Y. Kleiman L. Wainberg M.A. J. Virol. 1997; 71: 5750-5757Crossref PubMed Google Scholar,25Arts E.J. Ghosh M. Jacques P.S. Ehresmann B. Le Grice S.F.J. J. Biol. Chem. 1996; 271: 9054-9061Abstract Full Text Full Text PDF PubMed Scopus (61) Google Scholar, E.J. Li Y. Ehresmann B. Wainberg M.A. Le Grice S.F.J. S. A. 1996; PubMed Scopus Google Scholar, J. Virol. 1996; PubMed Google Scholar, 1996; PubMed Scopus Google Scholar, Y. Khorchid A. J. Wang J. Li X. Darlix Wainberg M.A. Kleiman L. J. Virol. 1998; PubMed Google Scholar, C. Keith G. Ehresmann B. Ehresmann C. Marquet R. Nucleic Acids Res. 1998; 26: PubMed Scopus Google Scholar). In this present a mutational analysis of the HIV-1 U5 leader stem. the of the mutant and in reverse transcription with the mutant RNA of HIV-1 with that the U5 region a motif that is critical for tRNA initiation of reverse transcription but not for that are by a primer. A of to this HIV-1 RNA motif in identified an sequence in the U5 region that is not in tRNA but that is for initiation of reverse transcription. that this motif with the TΨC arm of tRNA initiation of HIV-1 reverse transcription. This U5 motif, termed primer activation signal is masked in the wild-type RNA through base pairing in the U5 leader stem. reverse transcription can be by of the PAS through of the leader The of the PAS and a RNA structure provides a mechanism for positive and negative regulation of reverse transcription. In structure probing of the mutant and wild-type to the secondary structure of the PBS RNA secondary structure model is proposed in which the PAS and PBS motifs are regulation of reverse transcription in HIV-1 appears to be similar to that in RSV, that reverse transcription is regulated by a common mechanism in all retroviruses. A of the HIV-1 used to wild-type and U5 leader This been and a U5 region in the A.T. Klaver B. J.L.B. Berkhout B. J. Virol. 1997; 71: PubMed Google Scholar). to on HIV-1 with the For of the U5 leader stem, used the B. Berkhout B. J. Virol. 1994; PubMed Google Scholar), which of the and the of the to into The U5 leader stem by in with a in For sequence the leader region with the region primer to with the RNA polymerase sequence and the primer to with additional at its with the and an the into the which by sequence analysis of the in with at and with 1 of the HIV-1 by after to virus 1 to a in the by M. Essink B.B. Berkhout B. J. 1996; PubMed Scopus Google Scholar). The wild-type and mutant used as the for and in transcription. The region with the primer to with RNA polymerase sequence and the primer to The and in In transcription with the and the by through a the RNA and in The RNA by at for by to and the RNA at The RNA concentration by The in RNA with of tRNA of which tRNA with of primer in of at for for by to a that there is by tRNA 3Lys in this Essink B.B. Das A.T. Berkhout B. J. Mol. Biol. 1996; 264: 243-254Crossref PubMed Scopus (41) Google Scholar). the molecules not as a primer. The primer extended with 1 by the of of 1 of and of HIV-1 Reverse transcription for at in with and and of and of HIV-1 In the PBS the RNA with of tRNA and of primer, and reverse transcription in with avian virus enzyme The in and at in and on a The used are to to and to with additional at its with the to and primer with the and on the to the of the In HIV-1 leader RNA to with diethyl pyrocarbonate dimethyl sulfate in for at The and by The to and to used to the of with and The with the RNA in a of of for at and for at and to The primer extended by the of of and of avian virus enzyme in a at The with and on a by the on the to the of the of the U5 leader stem in reverse transcription, 1 a on of the U5 leader stem to and mutant a on the of the stem to The mutant A of to the stem of the U5 leader structure as in Fig. 1 C. The stem 1 by a on the in mutant on the in mutant and are and base pairing be in the mutant at to the RNA secondary structure model in Fig. Similar type of in stem and and and In the arm to and the arm to of the U5 leader structure in and in the mutant the of with U5 leader stem wild-type and mutant into the cell the and are for of the HIV-1 by the of in the at with 1 of the and that these virus that the U5 leader stem sequence by this region are for viral the of sequence structure in the of of stem 1 a on virus and in the virus and the mutant not in the stem also viral a on viral The of in mutant the not virus a and of the in mutant results that sequences stem of the U5 leader structure are for virus in reverse transcription with the wild-type and mutant HIV-1 RNA RNA the untranslated leader region to used with the tRNA 3Lys primer to initiate reverse transcription. The of the is in Fig. 1 A. The the RNA and reverse transcription by the of and HIV-1 reverse transcription and for the of RNA as with the primer are in Fig. The results of and are in Fig. reverse transcription of wild-type and and mutant The results of and the of the wild-type at is reverse transcription with the primer reverse transcription and The tRNA of the PBS is and also at 1 for the wild-type of the primer that is complementary to the PBS in a on the wild-type with a predicted in for the and to the in the U5 region The of reverse transcription is on all In of the tRNA primer, which results in a on the wild-type on the and and Fig. reverse transcription on the stimulated the wild-type in reverse transcription on the mutant from in tRNA initiation of reverse transcription, the reaction in the of but the other This in the of the tRNA with 1 on all The results of this initiation are similar to the results of initiation on the and a on the This that the of and the of are at the level of initiation. The in initiation may be by of tRNA primer the This the PBS motif is not in the mutant HIV-1 and the primer in these this the tRNA of the PBS on the wild-type and mutant The tRNA primer the and this subsequently used for of the primer that is downstream of the PBS 1 used the avian virus enzyme to the primer this enzyme is to the tRNA primer Essink B.B. Das A.T. Berkhout B. J. Mol. Biol. 1996; 264: 243-254Crossref PubMed Scopus (41) Google Scholar, N. F. Berkhout B. Nucleic Acids Res. 2000; PubMed Scopus Google Scholar). the PBS by the tRNA primer, reverse transcription by the a of RNA a of nts on the wild-type the that the are by the tRNA 3Lys primer with the upstream primer and the primer in the of tRNA The results of the PBS are in Fig. D. results a of positive and negative regulation of HIV-1 reverse transcription. The of the U5 leader stem to a sequence motif that is in initiation of reverse transcription. of the of the stem may this sequence motif, reverse transcription. are with the tRNA 3Lys primer and not with a PBS-bound primer, that additional may be The of stem to the sequence motifs that regulate HIV-1 reverse transcription. Reverse transcription with these mutant and the tRNA 3Lys primer. reverse transcription and for the of RNA as by primer The results of are in Fig. the in reverse transcription by the primer in in with in stem and reverse transcription with the wild-type tRNA and reverse transcription also stimulated reverse transcription and there is a on reverse transcription with the and the reverse transcription are for reverse transcription of wild-type and mutant The of and the of the wild-type at is reverse transcription reverse transcription tRNA of the PBS are at the level of initiation as in the tRNA The PBS that the tRNA primer is with in stem reverse transcription in a similar as the and of the of the stem reverse transcription, of the reverse transcription. results that the sequence the PBS-bound tRNA molecule to initiate reverse transcription. to this motif as the of the PAS in mutant reverse transcription, may initiation by the PAS also reverse transcription, which may that the of stem the of the stem The results an for the U5 leader stem, in for stem the secondary structure of the U5 leader stem by wild-type and mutant HIV-1 with to the and the are not to be in base pairing The of by primer in to of reverse transcription for RNA structure. The results of the probing on the wild-type are in Fig. RNA secondary structure model for the region of Based on structure probing this region is into the U5 leader stem, the and the PBS region. The for the are The proposed base pairing interaction between the HIV-1 PAS and in the TΨC arm of the tRNA 3Lys primer is in The interaction is of the wild-type with in of at and 1 and that are in the structure model of Fig. the that are proposed to be in stem 1 are also to that this part of the structure model is not of the wild-type with the and and and that A in the PBS region are In the A that are in stem 1 in Fig. highly to with and in in the PBS region and the arm of the U5 leader stem. also the at that are proposed to be in stem 1 1 and and results not results that the sequences proposed to be in base pairing in stem 1 are present in a the sequences in and are evidence for the of stem by probing of this in the mutant The of stem is not to in the wild-type 1 and on the the sequence on the of stem The and to that are from base pairing in mutant and In at in this In the mutant these are to and that base pairing in stem is In all other stem is not to results are with a RNA secondary structure model for the U5 leader stem that is in The U5 leader stem and are in this but shows the extended hairpin of stem 1 and the U5-PBS The that are to are in the loop of the and the A-rich loop of the U5-PBS hairpin is present as an The of stem 1 is present in the PBS region that is highly to and The A at and are to that are highly to and are present in loop of the arm of the U5 leader stem. Reverse transcription of the HIV-1 RNA genome appears to be strictly regulated at the level of initiation. analysis that the sequence on the of of the U5 leader stem is critical for initiation of reverse transcription but is in by tRNA of this motif in mutant results in a in reverse transcription. This sequence motif is not for of the tRNA primer the PBS but the of the to this sequence as the that the PAS sequence base with the TΨC arm of the tRNA molecule similar to the additional interaction proposed for the genome and the tRNATrp primer. The interaction not additional of the tRNA the TΨC the PAS sequence in the HIV-1 genome is by base pairing in the U5 leader stem, as by probing to be for the interaction with the tRNA primer. The of the PAS motif that is by base pairing provides a mechanism for positive and negative regulation of HIV-1 reverse transcription. with this reverse transcription is stimulated to by of the U5 leader stem in and that mutant in the mutant are of mutant in long these to a at the motif not This the that this interaction is for virus A similar interaction between a U5 motif in the genome of and the TΨC arm of the tRNATrp primer been to initiation of reverse transcription (22Aiyar A. Cobrinik D. Ge Z. Kung H.J. Leis J. J. Virol. 1992; 66: 2464-2472Crossref PubMed Google Scholar), and a similar vRNA-tRNA interaction also proposed for B. Schoneveld I. Nucleic Acids Res. 1993; 21: 1171-1178Crossref PubMed Scopus (58) Google Scholar). results that retroviral reverse transcription is by a common there are also between the HIV-1 and For the genome a similar U5 leader stem, the PAS is not in but in a region the PBS S. Leis J. J. Virol. 1999; 73: 6307-6318Crossref PubMed Google Scholar). This suggests that initiation of reverse transcription be by of the PAS motif, that regulation of reverse transcription may be in in that the structure of the U5 leader stem the U5 the the of the HIV-1 reported to the initiation of reverse transcription, that the sequence but that the structure (8Cobrinik D. Soskey L. Leis J. J. Virol. 1988; 62: 3622-3630Crossref PubMed Google Scholar, 9Cobrinik D. Aiyar A. Ge Z. Katzman M. Huang H. Leis J. J. Virol. 1991; 65: 3864-3872Crossref PubMed Google Scholar, 24Miller J.T. Ge Z. Morris S. Das K. Leis J. J. Virol. 1997; 71: 7648-7656Crossref PubMed Google Scholar). Similar that the structure of the U5 leader stem in HIV-1 to reverse transcription, by of the PAS In a that of the U5 leader stem initiation of reverse transcription and virus N. F. Berkhout B. Nucleic Acids Res. 2000; PubMed Scopus Google Scholar). of a virus that of stem by additional on the reverse transcription. results that the of HIV-1 reverse transcription is by the of the PAS and that the structure of the U5 leader stem can reverse transcription. Several between the tRNA 3Lys molecule and the HIV-1 RNA genome have been proposed on the of probing and (12Isel C. Ehresmann C. Keith G. Ehresmann B. Marquet R. J. Mol. Biol. 1995; 247: 236-250Crossref PubMed Scopus (229) Google Scholar, C. Keith G. Ehresmann B. Ehresmann C. Marquet R. Nucleic Acids Res. 1998; 26: PubMed Scopus Google Scholar, C. C. Le Grice S.F.J. Ehresmann B. Ehresmann C. Marquet R. J. 1999; PubMed Scopus Google Scholar). The A-rich loop of the U5-PBS hairpin proposed to interact with the anti-codon loop of tRNA 3Lys (12Isel C. Ehresmann C. Keith G. Ehresmann B. Marquet R. J. Mol. Biol. 1995; 247: 236-250Crossref PubMed Scopus (229) Google Scholar, 13Liang C. Li X. Rong L. Inouye P. Quan Y. Kleiman L. Wainberg M.A. J. Virol. 1997; 71: 5750-5757Crossref PubMed Google Scholar, E.J. Ghosh M. Jacques P.S. Ehresmann B. Le Grice S.F.J. J. Biol. Chem. 1996; 271: 9054-9061Abstract Full Text Full Text PDF PubMed Scopus (61) Google Scholar, E.J. Li Y. Ehresmann B. Wainberg M.A. Le Grice S.F.J. S. A. 1996; PubMed Scopus Google Scholar, J. Virol. 1996; PubMed Google Scholar, 1996; PubMed Scopus Google Scholar, Y. Khorchid A. J. Wang J. Li X. Darlix Wainberg M.A. Kleiman L. J. Virol. 1998; PubMed Google Scholar, C. Keith G. Ehresmann B. Ehresmann C. Marquet R. Nucleic Acids Res. 1998; 26: PubMed Scopus Google Scholar). In the arm of the U5 leader stem to to interact with the of the stem of the tRNA of these also by mutational analysis in in reverse transcription C. Rong L. M. Li X. Quan Y. Kleiman L. Wainberg M.A. J. Biol. Chem. 1998; Full Text Full Text PDF PubMed Scopus Google Scholar). mutant not to these the to motif is in mutant which shows a in reverse transcription. The interaction between the PAS and the TΨC arm of tRNA of the PAS motif results in a other vRNA-tRNA contacts, in to the and may to the initiation of reverse transcription. The critical of the PAS in tRNA is by recent in of the PAS and PBS motifs to tRNA the of the tRNA and B. in the PAS motif is all HIV-1 The RNA secondary structure probing in this an of the part of the U5 leader stem and the U5-PBS hairpin to the hairpin that the A-rich loop of the U5-PBS hairpin are present in an loop of the This RNA secondary structure model proposed (16Rizvi T.A. Panganiban A.T. J. Virol. 1993; 67: 2681-2688Crossref PubMed Google Scholar, 17Damgaard C.K. Dyhr-Mikkelsen H. Kjems J. Nucleic Acids Res. 1998; 26: 3667-3676Crossref PubMed Scopus (90) Google and is similar to the RNA structure model for B. Schoneveld I. Nucleic Acids Res. 1993; 21: 1171-1178Crossref PubMed Scopus (58) Google Scholar). In this RNA structure the PAS and PBS sequences are which may tRNA to motifs to initiation of reverse transcription. that RNA conformations a in of the viral For there is for the U5-PBS hairpin B. Schoneveld I. Nucleic Acids Res. 1993; 21: 1171-1178Crossref PubMed Scopus (58) Google Scholar, 23Berkhout B. Nucleic Acids Res. 1997; 25: 4013-4017Crossref PubMed Scopus (24) Google Scholar), and RNA conformations have been reported to for other of the HIV-1 leader RNA (18Berkhout B. vanWamel J.L.B. RNA (N. Y.). 2000; 6: 282-295Crossref PubMed Scopus (84) Google H.T. Berkhout B. RNA (N. Y.). 2001; 7: 143-157Crossref PubMed Scopus (180) Google Scholar). In a in the HIV-1 leader RNA to the U5-PBS hairpin N. Klaver B. Berkhout B. J. Virol. 2000; 74: 2227-2238Crossref PubMed Scopus (25) Google Scholar). of the U5-PBS hairpin virus and the of the tRNA primer the these also the hairpin of the U5-PBS hairpin virus and tRNA the with additional that the of the U5-PBS hairpin may of the is that the region upstream of the PBS a critical sequence that is as part of the by the viral D. R. J. 1998; PubMed Scopus Google Scholar, S. J. Virol. 1998; PubMed Google Scholar). are to into the of the U5-PBS hairpin A of this is that the wild-type HIV-1 RNA appears for in reverse transcription, as the initiation is by RNA secondary structure. that this mechanism may reverse transcription in the cell that the viral RNA genome is after is and into This mechanism reverse transcription to the the host cell from reverse transcription J. J. 1997; PubMed Scopus Google Scholar). with the wild-type and mutant that this of reverse transcription is also for virus The and reverse transcription in but virus are these also reverse transcription in in and particles. A is that these may also other in viral a The U5 leader region been reported to for viral A. J. G. M.A. J. Virol. 1994; PubMed Google Scholar, C. Rong L. Wainberg M.A. J. Virol. 2000; 74: PubMed Scopus Google Scholar). For this region reported to binding for transcription as part of the C. S. M. J. Virol. 1997; 71: PubMed Google Scholar, C. A. H. J. Virol. 1997; 71: PubMed Google Scholar, C. Li X. Quan Y. M. Kleiman L. J. Wainberg M.A. J. Mol. Biol. 1997; PubMed Scopus Google Scholar, A. G. R. M.A. Mol. Biol. 1998; PubMed Scopus Google Scholar). the of the on viral by virus in not transcription, and for and which virus and not This also to the of these which to the that may be to reverse transcription. of the PAS motif by base pairing may a mechanism to reverse transcription. binding of tRNA 3Lys to the PBS can in primer activation a of the vRNA-tRNA to the is that the viral nucleocapsid which as an RNA in A. 1998; Full Text Full Text PDF PubMed Scopus Google Scholar), can this is from the of this mechanism the for activation of reverse transcription. a in the HIV-1 leader which is mediated by H.T. Berkhout B. RNA (N. Y.). 2001; 7: 143-157Crossref PubMed Scopus (180) Google Scholar). extended of the U5 leader hairpin to the downstream RNA initiation which can subsequently be by This the that a RNA structure in the HIV-1 genome is used to the RNA that and primer This mechanism also that are by the for for critical of the and D. for the of HIV-1 enzyme through the