HIV-1 infection of non-dividing cells: Evidence that the amino-terminal basic region of the viral matrix protein is important for Gag processing but not for post-entry nuclear import

Human immunodeficiency virus type-1 (HIV-1) is able to infect non-dividing cells such as tissue macrophages productively because post-entry viral nucleoprotein complexes are specifically imported into the nucleus in the absence of mitosis. Although it has been proposed that an amino-terminal region of the viral matrix (MA, p17(Gag)) protein harbors a basic-type nuclear localization sequence (NLS) that contributes to this process, utilization of three distinct nuclear import assays failed to provide any direct supporting evidence. Instead, we found that disruption of this region (²⁶KK → TT) reduces the rate at which the viral Gag polyprotein (p55(Gag)) is post-translationally processed by the viral protease. Consistent with the fact that appropriate proteolytic processing is essential for efficient viral growth in all cell types, we also show that the ²⁶KK → TT MA mutation is equivalently deleterious to the replication of a primary macrophage-tropic viral isolate in cultures of non-dividing and dividing cells. Taken together, these observations suggest that proteins other than MA supply the NLS(s) that enable HIV-1 to infect non-dividing cells.