Human immunodeficiency virus type 1 Vpr protein transactivation function: Mechanism and identification of domains involved

The human immunodeficiency virus type 1 (HIV-1) Vpr protein is a virion-ass ociated protein that localizes in the nucleus of infected cells. Vpr has be en shown to facilitate HIV infection of non-dividing cells such as macropha ges by contributing to the nuclear translocation of the pre-integration com plex. More recently, Vpr expression has been shown to induce an accumulatio n of cells at the G2 phase of the cell-cycle. We have previously reported t hat Vpr stimulates reporter gene expression directed from the HIV-1 long te rminal repeat (LTR) as well as from heterologous viral promoters. However, the mode of action of Vpr-mediated transactivation remains to be precisely defined. We report here that, for a constant amount of transfected DNA, the level of chloramphenicol acetyltransferase (CAT) mRNA is increased in Vpr- expressing cells using either HIV-1 or a murine leukemia virus (MLV) SL3-3 LTR-CAT reporter construct. Moreover, this Vpr-mediated transactivation req uires that promoters direct a minimal level of basal expression. Our mutage nic analysis indicates that the transactivation mediated by Vpr is not depe ndent on the ability of the protein to localize in the nucleus or to be pac kaged in the virions. Interestingly, all transactivation-competent Vpr muta nts were still able to induce a cell-cycle arrest. Conversely, transactivat ion-defective mutants lost the ability to mediate cell-cycle arrest, implyi ng a functional relationship between these two functions. Overall, our resu lts indicate that the G2 cell-cycle arrest mediated by Vpr creates a cellul ar environment where the HIV-1 LTR is transcriptionally more active. (C) 19 98 Academic Press.