Bet counteracts the innate antiretroviral activity of APOBEC3 family defense factors by inhibiting their incorporation into virions. May be implicated in the establishment and/or maintenance of viral persistance. Bet is required for viral replication (By similarity). Bet binds to human APOBEC3F and APOBEC3G. Bet interacts with host APOBEC3C; this interaction does not induce APOBEC3C degradation, but prevents dimerization and incorporation into virion of the latter. Bet is highly expressed in infected cells, where it localizes to both cytoplasm and nucleus (PubMed:11884565). Also secreted and internalized by non-infected surrounding cells (PubMed:11884565). The first 88 residues are shared by isoform Bet and isoform Bel-1, the last 396 residues are shared by isoform Bet and isoform Bel-2.