Figure 4.

Selective growth of λ-HIVp in cells expressing cI.HIV. (A) The structure of the repressor-cro plasmid is illustrated. The expression of the cotransformed HIV protease was induced with IPTG (1 and 2 hr), and the cells were infected with λ. The graph illustrates the resulting phage titer/μl of culture supernatant. (B) Cells transformed with cI.HIV-cro or cI.HIVmt-cro cells were infected with λ-HIVp or λ-HIVinv for 5 hr. C1 and C2 are control infections of cells expressing cI.HIVmt. Experiments 1–4 and 5 and 6 are the resulting phage titers after one or three rounds of infection–selection in cI.HIV-cro cells, respectively. Fold-selective growth, pfu λ-HIVp/λ-HIVinv. As shown, selection in cI.HIV cells resulted in maintenance replication of λ-HIVp, whereas the replication of λ-HIVinv was inhibited more severely with each successive selection cycle.