POTENTIATION OF HUMAN-IMMUNODEFICIENCY-VIRUS TYPE-1 TAT BY HUMAN CELLULAR PROTEINS

The Tat protein is a potent activator of human immunodeficiency virus type 1 transcription. Tat has been shown to act by increasing both tra nscription initiation and elongation, but a detailed understanding of its interaction with the transcriptional machinery is lacking, With th e aim of isolating cellular proteins that interact with Tat and play a role in transactivation, we have reexamined its function in a cell fr ee transcription assay. Monitoring the appearance of transactivation a fter addition of purified Tat at intervals to the reaction mix reveale d a lag of approximately 10 min before Tat is able to effect transacti vation, incubation of Tat in nuclear or cytoplasmic extracts of human cells was sufficient to eliminate the lag, but nuclear extract from a rodent cell line was inactive. The accelerating effect of the human ce ll extract could be abrogated by dilution, heat inactivation, or chrom atographic depletion. We infer that Tat is potentiated for transactiva tion through interaction with a protein factor(s) that is specific to human cells.