A COFACTOR, TIP30, SPECIFICALLY ENHANCES HIV-1 TAT-ACTIVATED TRANSCRIPTION

Replication of HIV-1 requires the viral Tat protein, which increases t he extent of transcription elongation by RNA polymerase II after activ ation at the single viral long terminal repeat (LTR) promoter. This ef fect of Tat on transcription requires Tat interactions with a 5' regio n (TAR) in nascent transcripts as well as Tat-specific cofactors. The present study identifies a cellular protein, TIP30, that interacts wit h Tat and with an SRB-containing RNA polymerase II complex both in viv o and in vitro, Coexpression of TIP30 specifically enhances transactiv ation by Tat in transfected cells, and immunodepletion of TIP30 from n uclear extracts abolishes Tat-activated transcription without affectin g Tat-independent transcription, These results implicate TIP30 as a sp ecific coactivator that may enhance formation of a Tat-RNA polymerase II holoenzyme complex.