No G-to-A hypermutation in HTLV-1 genome was induced by APOBEC3G. Mutations in HTLV-1 and HIV-1 ΔVif viruses were detected by sequencing p12 and Env regions, respectively. G-to-A hypermutation was induced by APOBEC3G in HIV-1 ΔVif DNA, but not in HTLV-1 DNA. We detected very few G-to-A mutations in HTLV-1 K30 genome with expression of APOBEC3G (C), but not without expression of APOBEC3G (D), whereas G-to-A hypermutation was induced in HIV-1ΔVif DNA by APOBEC3G (A). We also detected a very few G-to-A mutations in MT-2/Mock virus DNA (E) as well as MT-2/Vif virus DNA (F). G-to-A mutations are shown in red, while other mutations are denoted in black. The numbers before the sequence indicate the number of each clone, while those in parentheses indicate the total number of clones sequenced. WT indicates no mutations in this region.