APOBEC3G is a single-strand DNA cytosine deaminase best understood as a potent inhibitor of HIV-1 replication [17] [18] [19] [20] [21] [22] [23] . It can however also inhibit a variety of other exogenous and endogenous retroviruses/elements (e.g., [17, 18, [24] [25] [26] [27] [28] [29] ). APO-BEC3G engages an assembling retrovirus particle, accesses the RNA genome-containing virus core and, upon reverse transcription, deaminates cDNA cytosines to uracils (C-to-U). Catastrophic levels of uracil either directly inactivate the coding capacity of the virus or trigger the degradation of the viral DNA. The former manifests as genomic strand-specific guanine to adenine (G-to-A) hypermutations (cDNA strand C-to-T transitions). However, in several instances, it is noteworthy that the deaminase activity of APOBEC3G or other APOBEC3 proteins is partly or even completely dispensable (e.g., HIV-1, hepatitis B virus, L1 and Alu [27] [28] [29] [30] [31] [32] ).