Enhancement of the p300 HAT activity by HIV-1 Tat on chromatin DNA

HIV-1 Tat is able to form a ternary complex with P/CAF and p300 and increas e the affinity for CDK9/P-TEFb CTD kinase complex. Our previous study demon strated that Tat binds to p300/CBP in the minimal HAT domain (aa 1253-1790) and that the interaction results in a change of conformation on p300/CBP. Here, we show that the Tat-p300 Interaction increases the HAT activity of p 300 on histone H4 that is associated with nucleosomal DNA and not with free histories, Nucleosomal histone H4 was acetylated on lysines 8, 12, and 16. Acetylation of H4 was inhibited by Lys-coenzyme A (CoA), a selective inhib itor of p300 acetyltransferase activity. Unexpectedly, we also found that T at could autoacetylate itself, which was specific to lysine residues 41 and 71. Peptides lacking these two lysines could not enhance the HAT activity of p300. Comparison of the sequences of Tat with other HIV-1 clades and HAT containing transcription factors indicated sequence identity in the acetyl -CoA binding motif A, KGXG. Furthermore, when utilizing an in vitro transcr iption assay, as well as a Tat mutant virus, we found that ectopic expressi on of only wild-type Tat in the presence of p300, and not a lysine 41 Tat m utant, could activate HIV-1 chromatin DNA, as evidenced by the absence of H IV-1 virion antigen. Therefore, transcription of integrated viral DNA in vi vo requires the HAT activity of coactivators that are modulated by Tat to d erepress the HIV-1 chromatin structure and aid in activated transcription. (C) 2001 Academic Press.