APOBEC3G (A3G) is a cytidine deaminase that functions as a potent innate immune restriction factor against retroviruses and retrotransposons 1. As a DNA deaminase, A3G catalyzes cytosine-to-uracil conversion in minus-strand viral DNA during reverse transcription, generating G-to-A hypermutations in the resulting proviral genome that cripple viral replication 1. This deamination-dependent mechanism works synergistically with a deamination-independent pre-integration pathway to collectively exert powerful antiretroviral effects 1. A3G selectively targets single-stranded DNA and demonstrates broad antiviral activity against HIV-1 (particularly Vif-deficient strains), SIV, HBV, EIAV, XMRV, and SFV 1. The protein localizes to P-bodies, cytoplasmic ribonucleoprotein complexes involved in mRNA processing, where it likely functions to restrict viral replication 2. HIV counters A3G through its Vif accessory protein, which binds A3G's negatively charged β4-α4 loop and mediates proteasomal degradation 3. Notably, APOBEC3G exhibits clinical relevance beyond virology: polymorphisms correlate with HPV persistence and cervical lesion progression 4, while A3G expression accelerates double-strand break repair and improves radiation resistance in vivo 5. Unexpectedly, A3G can paradoxically enhance HTLV-1 pathogenesis by activating TGF-β/Smad signaling 6.