Abstract
Akin to a ‘Trojan horse,’ APOBEC3G DNA deaminase is encapsulated by the HIV virion. APOBEC3G facilitates restriction of
HIV-1 infection in T cells by deaminating cytosines in nascent minus-strand complementary DNA. Here, we investigate the
biochemical basis for C-U targeting. We observe that APOBEC3G binds randomly to single-stranded DNA, then jumps and
slides processively to deaminate target motifs. When confronting partially double-stranded DNA, to which APOBEC3G cannot
bind, sliding is lost but jumping is retained. APOBEC3G shows catalytic orientational specificity such that deamination occurs
predominantly 3¢-5¢ without requiring hydrolysis of a nucleotide cofactor. Our data suggest that the G-A mutational gradient
generated in viral genomic DNA in vivo could result from an intrinsic processive directional attack by APOBEC3G on single-
stranded cDNA
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