The human immunodeficiency virus type 1 Vpr transactivator: cooperation with promoter-bound activator domains and binding to TFIIB.

Since the first report documenting that HIV-1 Vpr was involved in the stimulation of transactivation of several unrelated promoters, little additional information has been reported. By using transient transfection experiments, we confirmed and extended these previously reported data. Further in vivo experiments showed that Vpr can co-operatively stimulate transactivation activity of a minimal promoter containing one GAL4 DNA-binding site, when it is co-expressed with different heterologous activator domains fused to GAL4 DNA-binding domain. Thus, Vpr could transactivate in concert with an activator domain, but has no effect on the transactivation of a minimal promoter in the absence of activator protein. To investigate whether Vpr can interact with components of the basal transcriptional machinery, in vitro protein-protein binding assays were performed using either translated, radiolabeled Vpr or TFIIB proteins and glutathione S-transferase Vpr or TFIIB chimeric proteins. We demonstrated that the portion of Vpr ranging from amino acids 15 to 77 interacts specifically with the basal transcription factor TFIIB. Also, our data indicated that the N-terminal domain of TFIIB is required for the interaction.