Vif drives HIV-1–infected cells from G₁ into the S phase of the cell cycle. (A) Relative proportion of HeLa cells in the S phase compared with G₁ after cotransfection with GFP and pcDNA (white bars), wild-type NL4-3 (black bars), or NL4-3ΔVif (gray bars), along with GFP. Horizontal axis shows each transfection condition at 0, 1.5, and 3 hours after release from 24 hours of synchronization. The ratio of S/G₁ in cells transfected with NL4-3 was significantly increased compared with cells transfected with NL4-3ΔVif. (B) Ratio of number of cells in S compared with G₁ (S/G₁) in CEMss T cells 2 days after infection with wild-type NL4-3 or NL4-3ΔVif or mock infection. The mean ± SE of 3 experiments is shown. Infection levels, as measured by the percentage of Gag⁺ cells, were 0.1% ± 0.1% for mock, 51% ± 5.4% for NL4-3, and 55% ± 8.4% for NL4-3ΔVif. Significantly more cells entered the S phase when infected with the wild-type virus NL4-3 than with the wild-type virus deleted in Vif, NL4-3ΔVif (P < .05).