The virion infectivity factor (vif) is an accessory protein, which is essential for HIV replication in host cells. Vif of Human immunodeficiency virus 1 (HIV-1) affects the infectivity of virus particles []to T lymphocytes and macrophages (in some casesincreasing the infectivity of HIV-1 particles by 100- to 1000-fold), but has no direct effect on transcription, translation or virus release. Vif antibodies are found in the sera of patients at all levels of HIV-1 infection, indicating that vif is expressed in natural infections in vivo. Other lentiviruses, including Simian immunodeficiency virus (SIV-cpz), Visna/Maedi virus, and Feline immunodeficiency virus (FIV), have vif open reading frames, suggestingvif plays an essential role during natural infections [].The expression of vif in BHK-21 cells has been shown to be linked to amodification of the C terminus of gp41env, which modification is inhibited by trans-epoxysuccinyl-L-leucylamido-(4-guanidio)butane (E64), a specific inhibitor of cysteine proteases []. Coupled with sequence analysis and the effects of point mutations in vif, it has been suggested that vif could be a cysteine protease. Virions produced in the absence of Vif have abnormal core morphology and those produced in primary T cells carry immature core proteins and low levels of mature capsid [].In humans, HIV-1 Vif hijacks cellular E3 ligase components containing CUL5, RBX2, ELOB, ELOC and CBFbeta, to poly-ubiquitinate antiviral cellular factors, APOBEC3 proteins [, , ]. In sheep and goats, Caprine arthritis encephalitis virus (CAEV) Vif is responsible for degradation of oaA3Z2-Z3 [].
