INTERACTION BETWEEN THE CYTOPLASMIC DOMAINS OF HIV-1 VPU AND CD4 - ROLE OF VPU RESIDUES INVOLVED IN CD4 INTERACTION AND IN-VITRO CD4 DEGRADATION

The Vpu and CD4 cytoplasmic domains were found, by using a two-hybrid assay in yeast, to interact in the absence of their membrane anchor do mains. Studies on several deletion and point mutants revealed that the overall structure of the Vpu cytoplasmic domain is required for this interaction. The Vpu amino acid residues involved in the interaction w ith CD4 were identified. Deletion of the C-terminal residues of Vpu, r equired for CD4 degradation, as well as the double mutation on the cas ein kinase II phosphorylation sites S52N-S56N, also involved in CD4 de gradation, resulted in the loss of interaction with CD4 and in the ina bility to induce CD4 degradation. These results suggest that the abili ty of Vpu to mediate the degradation of CD4 is linked to its capacity to physically interact with CD4. However, additional mutagenesis on th e S52 site revealed that the interaction between the cytoplasmic domai ns of Vpu and CD4 is not sufficient for in vitro Vpu-mediated CD4 degr adation. (C) 1996 Academic Press, Inc.