Ction of target cells, the gRNA is copied by the viral Reverse Transcriptase (RT) to generate the viral DNA in a process called Reverse Transcription (RTion). It is a multistep process initiated from a cellular tRNA annealed to the 59 end PBS (Primer Binding Site) of the gRNA and subsequently requires two DNA strand transfers to synthesize the complete double-stranded viral DNA flanked by the two long terminal repeats (LTR). Several steps of RTion 60940-34-3 require nucleic acids remodeling reactions that are chaperoned by NC, notably primer tRNA annealing to the PBS and the two obligatory DNA strand transfers (for review see [19,20,21]. Viral DNA synthesis can occur during retrovirus assembly 
as shown for RSV, MuLV and HIV-1, but at low level ([22,23,24]. Recently, mutations in the NC basic residues and ZFs were found to cause extensive RTion in the course of virusRoles of the NC in HIV-1 and MuLV Replicationsassembly in HIV-1 producing cells [25,26]. Similarly to HBV and foamy viruses, we called this process “late RTion”. Thus, our data further support a role for NC in the control of RTion and its timing throughout the HIV-1 replication cycle [27,28]. Yet it is not known whether the involvement of NC in the timing of RTion is specific for HIV-1 or is also valid for other retroviruses, such as alpha- and gammaretroviruses with diverse NCs. Late RTion was maximal when HIV-1 NC contained only the proximal ZF (ZF1) without ZF2 (DZF2), indicating that the two ZFs of HIV-1 are not functionally equivalent [26,29]. However, MuLV has a unique NC ZF that is critical for RTion [30,31]. To get a better understanding of the role of NC in the late steps of MuLV 
replication, we asked whether the conserved features of MuLV NC, the basic residues and the unique ZF, are functionally equivalent to those of HIV-1 NC (Fig 1). We revisited by quantitative RT-PCR and PCR analyses the role of MuLV NC in gRNA packaging and we asked whether the basic residues and/ or the unique ZF could control RTion during virus assembly. To this end, we studied the impact of mutating or deleting these conserved domains of MuLV NC. Our results show that the basic residues and the unique ZF play a major role in gRNA packaging, and the basic residues (aa16?3, Fig 1) are important determinant for virus release, underlying the similarity between MuLV and HIV NC’s. In contrast, MuLV NC, unlike HIV-1 NC, did not influence late RTion since mutating MuLV NC did not cause the accumulation of a high level of viral DNA in mutant virions.Materials and Methods Plasmids and mutagenesisThe molecular clones pRR88-wt, pRR88-C39S, pRR88-D16?23 of Mo-MuLV were provided by A. Rein and previously buy 3PO described in [11,13,32]. The MuLV molecular clone PR- contains a deletion of the protease (nt 2421?2546) as previously described [33]. The pRR88-DZF was constructed by substitution of the XhoI-SalI fragment (nt 15755315 1560 to 7674 of MuLV) that was previously inserted in a pSP72 vector and mutated with the QuikChangeH Lightning Site-Directed Mutagenesis Kit (Stratagene) according to the manufacturer’s instructions. The mutated oligonucleotides used were sense-DZF (59-CCCAACTCGATCGCGACAAGAAACCACGAGGA) and antisense-DZF (59-CCTCGTGGTTTCTTGTCGCGGATCGAGTTGGG) to generate construct with deletion of ZF (nt 2127?174). 23115181 All constructs were confirmed by sequencing. The HIV-1 pNL4? molecular clone was used to generate the mutant DZF2 with harbors a deletion of the second zinc finger motif of the NC. As previouly described [34], th.Ction of target cells, the gRNA is copied by the viral Reverse Transcriptase (RT) to generate the viral DNA in a process called Reverse Transcription (RTion). It is a multistep process initiated from a cellular tRNA annealed to the 59 end PBS (Primer Binding Site) of the gRNA and subsequently requires two DNA strand transfers to synthesize the complete double-stranded viral DNA flanked by the two long terminal repeats (LTR). Several steps of RTion require nucleic acids remodeling reactions that are chaperoned by NC, notably primer tRNA annealing to the PBS and the two obligatory DNA strand transfers (for review see [19,20,21]. Viral DNA synthesis can occur during retrovirus assembly as shown for RSV, MuLV and HIV-1, but at low level ([22,23,24]. Recently, mutations in the NC basic residues and ZFs were found to cause extensive RTion in the course of virusRoles of the NC in HIV-1 and MuLV Replicationsassembly in HIV-1 producing cells [25,26]. Similarly to HBV and foamy viruses, we called this process “late RTion”. Thus, our data further support a role for NC in the control of RTion and its timing throughout the HIV-1 replication cycle [27,28]. Yet it is not known whether the involvement of NC in the timing of RTion is specific for HIV-1 or is also valid for other retroviruses, such as alpha- and gammaretroviruses with diverse NCs. Late RTion was maximal when HIV-1 NC contained only the proximal ZF (ZF1) without ZF2 (DZF2), indicating that the two ZFs of HIV-1 are not functionally equivalent [26,29]. However, MuLV has a unique NC ZF that is critical for RTion [30,31]. To get a better understanding of the role of NC in the late steps of MuLV replication, we asked whether the conserved features of MuLV NC, the basic residues and the unique ZF, are functionally equivalent to those of HIV-1 NC (Fig 1). We revisited by quantitative RT-PCR and PCR analyses the role of MuLV NC in gRNA packaging and we asked whether the basic residues and/ or the unique ZF could control RTion during virus assembly. To this end, we studied the impact of mutating or deleting these conserved domains of MuLV NC. Our results show that the basic residues and the unique ZF play a major role in gRNA packaging, and the basic residues (aa16?3, Fig 1) are important determinant for virus release, underlying the similarity between MuLV and HIV NC’s. In contrast, MuLV NC, unlike HIV-1 NC, did not influence late RTion since mutating MuLV NC did not cause the accumulation of a high level of viral DNA in mutant virions.Materials and Methods Plasmids and mutagenesisThe molecular clones pRR88-wt, pRR88-C39S, pRR88-D16?23 of Mo-MuLV were provided by A. Rein and previously described in [11,13,32]. The MuLV molecular clone PR- contains a deletion of the protease (nt 2421?2546) as previously described [33]. The pRR88-DZF was constructed by substitution of the XhoI-SalI fragment (nt 15755315 1560 to 7674 of MuLV) that was previously inserted in a pSP72 vector and mutated with the QuikChangeH Lightning Site-Directed Mutagenesis Kit (Stratagene) according to the manufacturer’s instructions. The mutated oligonucleotides used were sense-DZF (59-CCCAACTCGATCGCGACAAGAAACCACGAGGA) and antisense-DZF (59-CCTCGTGGTTTCTTGTCGCGGATCGAGTTGGG) to generate construct with deletion of ZF (nt 2127?174). 23115181 All constructs were confirmed by sequencing. The HIV-1 pNL4? molecular clone was used to generate the mutant DZF2 with harbors a deletion of the second zinc finger motif of the NC. As previouly described [34], th.