FIG. 2.

Schematic drawing showing the structure of the pHIV1-SH vector. (A) pHIV1-SH. The viral genes gag and pol and partially deleted env are shown (not to scale). The cassette is indicated by a box with slashes. (B) Schematic representation of the cassette and the mutants. Mutations are indicated in bold. The virus titers, normalized to the luciferase activity, are shown relative to that of the WT virus. These results are the averages from three independent experiments. Pol II, murine RNA Pol II promoter; EM-Zeo, EM-7 promoter-zeocin resistance gene; lacO, lac operator. A nonviral sequence derived from the parental vector is indicated by a small black box at the right end of the drawing. (C) Schematic numbering of the nucleotide positions in the LTR termini of the circles derived from autointegration events.