Lack of infectivity of HIV-1 integrase zinc finger-like domain mutant with morphologically normal maturation.

The integrase (IN) encoded by human immunodeficiency virus type-1 (HIV-1) is required for integration of the viral DNA into a host cell chromosome. The function of the highly conserved HHCC motif in the HIV-1 IN amino-terminal zinc finger-like domain is still unknown. In this study, we examined the effect of mutations in the HHCC motif on viral infectivity, adsorption to and entry into target cells, and morphology in the context of a full-length form of an HIV-1 molecular clone. A complete lack of infectivity and de novo synthesized viral DNA of the HHCC mutants were demonstrated in both cell-free and co-culture infection systems using MT-2 or HeLa-CD4-LTR-beta-gal as target cells. The levels of viral adsorption to and entry into the target cells were determined by measuring the cell-associated p24 level in target MT-2 cells shortly after infection. We detected comparable cell-associated p24 levels of MT-2 cells after infection with wild-type and the mutant viruses. Taken together, these results suggest that the replication of HIV-1 carrying point mutations in the HHCC motif was blocked at the step after adsorption/ entry and prior to the initiation of reverse transcription, presumably at the uncoating step. Furthermore, electron microscopy revealed that the observed complete lack of viral infectivity caused by introducing an amino acid substitution into the HHCC motif is not always accompanied by apparent abnormal morphology or maturation of virus particles.