FIG. 3.

Absence of mutations in the vif gene of multiply passaged chronically infected H9 cells. Genomic DNA from H9/HXB2NEO and H9/HXB2VifΔNEO cells was prepared from 10⁷ cells and used for PCR amplification of the proviral vif genes. PCR products were purified and cloned into the EcoRI and BamHI sites of the in vitro transcription vector pSP65. Two independent clones were sequenced for each of the Vif⁺ [Vif(+)] or Vif⁻ [Vif(−)] variants. The translated Vif sequence was aligned against the published HXB2 Vif sequence. No sequence variation was observed for any of the wild-type Vif sequences. As predicted, the Vif⁻ provirus carries a 68-bp out-of-frame deletion that results in a frameshift at residue 28 in Vif followed by six nonsense residues (not shown) and premature termination.