Human cytidine deaminases APOBEC3G (A3G) and APOBEC3F (A3F) inhibit replication 
of Vif-deficient human immunodeficiency virus type 1 (HIV-1). HIV-1 Vif 
overcomes these host restriction factors by binding to them and inducing their 
proteasomal degradation. The Vif-A3G and Vif-A3F interactions are attractive 
targets for antiviral drug development because inhibiting the interactions could 
allow the host defense mechanism to control HIV-1 replication. It was recently 
reported that the Vif amino acids D(14)RMR(17) are important for functional 
interaction and degradation of the previously identified Vif-resistant mutant of 
A3G (D128K-A3G). However, the Vif determinants important for functional 
interaction with A3G and A3F have not been fully characterized. To identify 
these determinants, we performed an extensive mutational analysis of HIV-1 Vif. 
Our analysis revealed two distinct Vif determinants, amino acids Y(40)RHHY(44) 
and D(14)RMR(17), which are essential for binding to A3G and A3F, respectively. 
Interestingly, mutation of the A3G-binding region increased Vif's ability to 
suppress A3F. Vif binding to D128K-A3G was also dependent on the Y(40)RHHY(44) 
region but not the D(14)RMR(17) region. Consistent with previous observations, 
subsequent neutralization of the D128K-A3G antiviral activity required 
substitution of Vif determinant D(14)RMR(17) with SEMQ, similar to the SERQ 
amino acids in simian immunodeficiency virus SIV(AGM) Vif, which is capable of 
neutralizing D128K-A3G. These studies are the first to clearly identify two 
distinct regions of Vif that are critical for independent interactions with A3G 
and A3F. Pharmacological interference with the Vif-A3G or Vif-A3F interactions 
could result in potent inhibition of HIV-1 replication by the APOBEC3 proteins.