Mutational analysis of Vpr-induced G2 arrest, nuclear localization, and cell death in fission yeast

Cell cycle G(2) arrest, nuclear localization, and cell death induced by human immunodeficiency virus type 1 Vpr were examined in fission yeast by using a panel of Vpr mutations that have been studied previously in human cells. The effects of the mutations an Vpr functions were highly similar between fission yeast and human cells. Consistent with mammalian cell studies, induction of cell cycle G(2) arrest by Vpr was found to be independent of nuclear localization. In addition, G(2) arrest was also shown to be independent of cell killing, which only occurred when the mutant Vpr localized to the nucleus. The C-terminal end of Vpr is crucial for G(2) arrest, the N-terminal alpha-helix is important for nuclear localization, and a large part of the Vpr protein is responsible for cell killing. It is evident that the overall structure of Vpr is essential for these cellular effects, as N- and C-terminal deletions affected all three cellular functions. Furthermore, two single point mutations (H33R and H71R), both of which reside at the end of each alpha-helix, disrupted all three Vpr functions, indicating that these two mutations may have strong effects on the overall Vpr structure. The similarity of the mutant effects on Vpr function in fission yeast and human cells suggests that fission yeast can be used as a model system to evaluate these Vpr functions in naturally occurring viral isolates.