The karyophilic properties of human immunodeficiency virus type 1 integrase are not required for nuclear import of proviral DNA.

Integrase (IN) is a key component of the preintegration nucleoprotein complex (PIC), which transports the retroviral genome from the cytoplasm to the nucleus of newly infected cells. Retroviral IN proteins have intrinsic karyophilic properties, which for human immunodeficiency virus type 1 (HIV-1) are currently attributed to regions that display sequence homology to previously characterized nuclear localization signals. We asked here whether the karyophilic properties of HIV-1 IN are involved in the nuclear import of PIC. We mutated three conserved basic regions in the C-terminal domain of IN and analyzed the effects of mutations on subcellular localization of the protein, viral particle composition, IN dimerization within virions, and infectivity. Alteration of two sequences caused the loss of nuclear accumulation of IN and drastically reduced the capacity of the protein to multimerize. Mutation of the most C-terminal sequence had no effect on the subcellular localization and dimerization of IN. Nevertheless, conservation of all three sequences was required for viral infectivity. Despite the perturbation of IN subcellular localization, all mutant viruses displayed normal reverse transcription and nuclear transport of PICs in newly infected cells. The replicative defect was instead at the level of integration, for which all mutants were markedly affected in vivo. Besides reinforcing the association between dimerization of IN and nuclear accumulation of the enzyme, our data demonstrate that subcellular localization of IN alone cannot predict the fate of the PICs.