Nucleic acids content of wild-type and NC mutant HIV-1 virions. WT, ΔZF1, ΔZF2 and ΔZF1ZF2 represent wild type, and deletion of the first, the second and of both CCHC zinc fingers, respectively. All values were determined by quantitative RT-PCR (A) and PCR (B) (n = 3 ± SD). A- Viral RNAs corresponding to the full length (FL) and the multispliced (MS) forms. B- Viral DNAs corresponding to the strong stop (ss), Gag, full length (FL) and mutispliced (MS) forms.

A scheme of the HIV-1 replication complex. The genomic RNA in a dimeric form is coated by about 1500 nucleocapsid (NC) protein molecules (in red) in the viral core particle. Molecular interactions have been characterized, at least in part, namely (i) the two viral RNAs via DIS, DLS, 5'-3' and other interactions to form the dimeric 60S complex (black lines), (ii) the primer tRNALys3 (thin black line) annealed to the viral PBS RNA, (iii) NC molecules coating the viral RNA and tRNA (NC basic residues and zinc fingers), (iv) the primer tRNALys3 bound to RTp66-p51(in blue), (v) the viral RNA and RT, (vi) NC and RT and (vii) NC and NC molecules. Viral proteins such as IN and Vif that may play a role in viral DNA synthesis are not represented in this scheme. For references see text.

A proposed mechanism for late reverse transcription in cells producing HIV-1 NC mutant particles. A- Newly made Gag and GagPol molecules (1) assemble using the genomic RNA and cellular membrane as platforms, (2) then wild type HIV-1 virions are produced by budding. These processes are facilitated by interactions between NC and cellular proteins (large black arrows). The core containing the genomic RNA is condensed with a cone-shaped structure. A limited level of viral DNA synthesis in producer cells and also anatural endogenous reverse transcription (NERT) can occur (see text). B- In cells producing HIV-1 Gag and GagPol with mutation in or deletion of the nucleocapsid CCHC zinc finger (1), assembly (2) and budding (grey arrow) are probably slowed down due to impaired interactions between NC and the viral RNA. They result in a partial delocalization of Gag in producer cells and a reduced level of newly made viral particles (grey arrow) (see text for references). The resulting virion core is formed of mature Gag proteins, but it is poorly condensed as seen by electron microscopy (see text for references). Taken together, these observations favor the notion that the NC CCHC mutations modify the kinetics of viral assembly which prevent core condensation and could explain, at least in part, why late-premature reverse transcription can readily take place in producer cells.