APOBEC3B and HIV-1 infection: Importantly, APOBEC3B (A3B) is constitutively localized in the nucleus (Muckenfuss et al., 2006) and inhibits HIV-1 infection independent of the presence of Vif, which otherwise counteracts the activity of the remaining A3 family members (Bishop et al., 2004; Doehle et al., 2005).