Inhibition of HTLV-1 infection by APOBEC3G. APOBEC3G as well as its mutants inhibited the infectivity of HTLV-1. Infectivity of HTLV-1 was measured as described in Materials and Methods. HTLV-1 proviral DNA load in target SupT1 cells was suppressed by APOBEC3G and its mutants to the level of that of heat-inactivted virus. Six independent experiments gave similar results and the data was presented as the mean of these values. Values are presented as infectivity ratio relative to K30 virus without expression of APOBEC3G.