A cofactor, TIP30, specifically enhances HIV-1 Tatactivated transcription

^*Laboratory of Biochemistry and Molecular Biology, The Rockefeller University, New York, NY 10021; and ^†Banting and Best Department of Medical Research and Department of Molecular and Medical Genetics, University of Toronto, Ontario, Canada M5G 1L6

Contributed by Robert G. Roeder

Abstract

Replication of HIV-1 requires the viral Tat protein, which increases the extent of transcription elongation by RNA polymerase II after activation at the single viral long terminal repeat (LTR) promoter. This effect of Tat on transcription requires Tat interactions with a 5′ region (TAR) in nascent transcripts as well as Tat-specific cofactors. The present study identifies a cellular protein, TIP30, that interacts with Tat and with an SRB-containing RNA polymerase II complex both in vivo and in vitro. Coexpression of TIP30 specifically enhances transactivation by Tat in transfected cells, and immunodepletion of TIP30 from nuclear extracts abolishes Tat-activated transcription without affecting Tat-independent transcription. These results implicate TIP30 as a specific coactivator that may enhance formation of a Tat–RNA polymerase II holoenzyme complex.

Footnotes

↵ ‡ To whom reprint requests should be addressed. e-mail: roeder{at}rockvax.rockefeller.edu.
Data deposition: The sequence reported in this paper has been deposited in the GenBank database (accession no. AF039103).
ABBREVIATIONS:

GST,

glutathione S-transferase;

CTD,

carboxyl-terminal domain;

TAK,

Tat-associated kinase;

HA,

hemagglutinin;

CAT,

chloramphenicol acetyltransferase;

LTR,

long terminal repeat