To determine whether DNA deamination is required the APOBEC3G-dependent inhibition of PERV transmission, we established a new set of PK-15 clones expressing APOBEC3G, APOBEC3G E259Q or a vector control (Figure 4, inset) . Surprisingly, both APOBEC3G and the E259Q derivative diminished PERV transmission to near background levels ( Figure 4) . These data demonstrated that the mechanism of inhibition does not require the DNA deaminase activity of APOBEC3G. These data were further supported by the fact that plus strand G-to-A hypermutations were not apparent in the DNA of the rare transmission events that occurred in the presence of human APOBEC3G (below).