Fig. 6. Exchange at amino acid 128 is sufficient to switch the virion infectivity factor (Vif) interaction specificity. Luciferase reporter viruses were generated in the presence of increasing amounts of APOBEC3G. 293T cells were cotransfected with 2 m g of HIV-1 or SIV_AGM luciferase reporter virus plasmid, 1 m g of pcVSV-G, and the increasing amounts of APOBEC3G expression vector as indicated on the x axis. Infectivity of equivalent amounts of virus was measured on HOS.CD4 cells. External oligonucleotides for overlapping PCR of APOBEC3G: CEM15-CM1, TAA GCG GAA TTC GGC CCT GGG AGG TCA CTT TAG GG; CEM15 HA-C, TAG AAG CTC GAG TCA AGC GTA ATC TGG AAC ATC GTA TGG ATA GTT TTC CTG ATT CTG GAG.