As previously described [26]. In contrast to HIV-1, the viral cDNA was not found in cellular DNA samples (data not shown). These results are consistent with those on the virion viral DNA content and indicate the absence of active late RTion in MuLV producer cells (Fig 4B).69056-38-8 Analysis of the coexpression of MuLV and HIV-MuLV and HIV-1 NCs have similar functions in assembly which is further highlighted by the production of chimeric MuLVHIV-1 VLPs. In addition, the HIV NC can recognize the MuLV RNA genome although less efficiently than the HIV-1 gRNA [12,45]. Based on these observations, we wanted to examine whether in the context of complete viruses, the expression 12926553 of the DZF2 HIV-1 mutant, which 223488-57-1 biological activity produced DNA-containing particles,could confer late RTion activity to MuLV. HIV-1 DZF2 NC could recognize the MuLV gRNA, causing its reverse transcription as for the HIV-1 gRNA. To this end, MuLV was cotransfected with the wt or DZF2 HIV-1 molecular clone (pNL4-3). No HIV tracer was added to the supernatants during these assays. First, we examined the particles released by Western immunoblotting with anti-CA antibodies specific for MuLV or HIV-1 (Fig 5A). Surprisingly, MuLV production was impaired in presence of the DZF2 HIV-1 mutant, but not by the wt HIV-1. In contrast, DZF2 HIV-1 production remained unchanged with or without MuLV. Then, we analyzed the DNA content of the released particles. Examination of MuLV DNA in virion released when MuLV and DZF2 were coexpressed, showed a reduction of the intravirion DNA (Fig 5B). This result correlates with the failure to release virions (Fig 5A). Upon MuLV expression, the level of HIV-1 intravirion DNA was higher in presence of DZF2 HIV-1 than with wt HIV-1 (7.5-fold). However, in previous experiments with HIV1 alone (Fig 4C) the maximum differences observed between the DZF2 and wt HIV-1 were about 100-fold. These results suggest that the presence of MuLV impaired the late RTion activity of the mutant HIV-1 (DZF2).DiscussionNC is involved in the RTion reation with at least two key partners, 23727046 the RT enzyme and the genomic RNA template (gRNA). In fact, NC molecules extensively coat the gRNA to form the nucleocapsid structure (Darlix et al., 1995; 2011) where tight interactions take 
place between NC molecules, the cellular tRNARoles of the NC in HIV-1 and MuLV ReplicationsFigure 5. Coproduction of MuLV and HIV-1 virions. Supernatant were collected from cells cotransfected with MuLV and wt or DZF2 HIV-1 molecular clones (MuLV:HIV ratio of 1:3). Released virions were pelleted and proteins analyzed by Western blotting (A). The same blot was used to probe the MuLV and HIV-1 CA proteins. The intravirion levels of MuLV and HIV-1 DNA were determined and calculated as in Fig 4C (B). doi:10.1371/journal.pone.0051534.gprimer and the RT enzyme [2]. The role of NC in RTion largely relies on its nucleic acid chaperone activity, i.e. the ability to direct nucleic acid conformational rearrangements [40,46]. Moreover, NC exerts a control over the timing of RTion, in a spatio-temporal manner. Indeed, mutating the N-terminal basic residues or the zinc finger motifs (ZF) of HIV-1 NC caused late RTion in HIV-1 producer cells with a 10?00 fold enhancement of newly made viral DNA found in virions as compared with wild-type virions [25,26,43]. How HIV-1 controls this late RTion activity remains a matter of debate. However, inactivating the HIV-1 protease or slowing down virus release modulates intravirion DNA levels in such HIV-1.As previously described [26]. In contrast to HIV-1, the viral cDNA was not found in cellular DNA samples (data not shown). These results are 
consistent with those on the virion viral DNA content and indicate the absence of active late RTion in MuLV producer cells (Fig 4B).Analysis of the coexpression of MuLV and HIV-MuLV and HIV-1 NCs have similar functions in assembly which is further highlighted by the production of chimeric MuLVHIV-1 VLPs. In addition, the HIV NC can recognize the MuLV RNA genome although less efficiently than the HIV-1 gRNA [12,45]. Based on these observations, we wanted to examine whether in the context of complete viruses, the expression 12926553 of the DZF2 HIV-1 mutant, which produced DNA-containing particles,could confer late RTion activity to MuLV. HIV-1 DZF2 NC could recognize the MuLV gRNA, causing its reverse transcription as for the HIV-1 gRNA. To this end, MuLV was cotransfected with the wt or DZF2 HIV-1 molecular clone (pNL4-3). No HIV tracer was added to the supernatants during these assays. First, we examined the particles released by Western immunoblotting with anti-CA antibodies specific for MuLV or HIV-1 (Fig 5A). Surprisingly, MuLV production was impaired in presence of the DZF2 HIV-1 mutant, but not by the wt HIV-1. In contrast, DZF2 HIV-1 production remained unchanged with or without MuLV. Then, we analyzed the DNA content of the released particles. Examination of MuLV DNA in virion released when MuLV and DZF2 were coexpressed, showed a reduction of the intravirion DNA (Fig 5B). This result correlates with the failure to release virions (Fig 5A). Upon MuLV expression, the level of HIV-1 intravirion DNA was higher in presence of DZF2 HIV-1 than with wt HIV-1 (7.5-fold). However, in previous experiments with HIV1 alone (Fig 4C) the maximum differences observed between the DZF2 and wt HIV-1 were about 100-fold. These results suggest that the presence of MuLV impaired the late RTion activity of the mutant HIV-1 (DZF2).DiscussionNC is involved in the RTion reation with at least two key partners, 23727046 the RT enzyme and the genomic RNA template (gRNA). In fact, NC molecules extensively coat the gRNA to form the nucleocapsid structure (Darlix et al., 1995; 2011) where tight interactions take place between NC molecules, the cellular tRNARoles of the NC in HIV-1 and MuLV ReplicationsFigure 5. Coproduction of MuLV and HIV-1 virions. Supernatant were collected from cells cotransfected with MuLV and wt or DZF2 HIV-1 molecular clones (MuLV:HIV ratio of 1:3). Released virions were pelleted and proteins analyzed by Western blotting (A). The same blot was used to probe the MuLV and HIV-1 CA proteins. The intravirion levels of MuLV and HIV-1 DNA were determined and calculated as in Fig 4C (B). doi:10.1371/journal.pone.0051534.gprimer and the RT enzyme [2]. The role of NC in RTion largely relies on its nucleic acid chaperone activity, i.e. the ability to direct nucleic acid conformational rearrangements [40,46]. Moreover, NC exerts a control over the timing of RTion, in a spatio-temporal manner. Indeed, mutating the N-terminal basic residues or the zinc finger motifs (ZF) of HIV-1 NC caused late RTion in HIV-1 producer cells with a 10?00 fold enhancement of newly made viral DNA found in virions as compared with wild-type virions [25,26,43]. How HIV-1 controls this late RTion activity remains a matter of debate. However, inactivating the HIV-1 protease or slowing down virus release modulates intravirion DNA levels in such HIV-1.