Amino acid residues 88 and 89 in the central hydrophilic region of human immunodeficiency virus type 1 Vif are critical for viral infectivity by enhancing the steady-state expression of Vif

A hydrophilic region consisting of strikingly clustered charged amino acids is present at the center of human immunodeficiency virus type I (HIV-1) Vif. In this study, the role for this central hydrophilic region ((EWRKKR93)-W-88) in the virus replication in nonpermissive H9 cells was investigated by extensive deletion and substitution analysis. A total of 31 mutants were constructed. Deletion of the E-88 or W-89 residue alone abolished viral infectivity in H9 cells and impaired virus replication in primary macrophage cultures. Substitution analysis indicated that the hydrophilicity and charge of the central region are insignificant for the function of Vif. Of the 16 substitution mutants, 3 mutants with substitution of E-88 and W-89 with an A residue did not grow in H9 cells. Upon transfection, four mutants (i.e., two mutants with deletion of E-88 or W-89; a mutant with substitution of E-88 and W-89 with A; and a mutant with substitution of E-88, W-89, and R-90 with A) were found to express Vif at a very reduced level relative to that by the wild-type clone. These results have thus demonstrated that amino acid residues 88 and 89 of Vif are critical for the replication of HIV-1 in target cells by enhancing the steady-state expression of Vif. In addition, E-88 and W-89 residues were found to be extremely conserved among the Vif proteins of naturally occurring HIV-1 field isolates as well as those of laboratory HIV-1 strains.