THE ACETYLTRANSFERASE ACTIVITY OF CBP STIMULATES TRANSCRIPTION

The CBP co-activator protein possesses an intrinsic acetyltransferase (AT) activity capable of acetylating nucleosomal histones, as well as other proteins such as the transcription factors TFIIE and TFIIF, In a ddition, CBP associates with two other TSs, P/CAF and SRC1, We set out to establish whether the intrinsic AT activity of CBP contributes to transcriptional activation. We show that a region of CBP, encompassing the previously defined histone AT (HAT) domain, can stimulate transcr iption when tethered to a promoter. The stimulatory effect of this act ivation domain shows some promoter preference and is dependent on AT a ctivity. Analysis of 14 point mutations reveals a direct correlation b etween CBP's ability to acetylate histones in vitro and to activate tr anscription in vivo. We also find that the HAT domains of CBP and P/CA F share sequence similarity. Four conserved motifs are identified, thr ee of which are analogous to motifs A, B and D, found in other N-acety ltransferases. The fourth motif, termed E, is unique to CBP and P/CAF, Mutagenesis shows that all four motifs in CBP contribute to its HAT a ctivity ill vitro and its ability to activate transcription in vivo. T hese results demonstrate that the AT activity of CBP is directly invol ved in stimulating gene transcription. The identification of specific HAT domain motifs, conserved between CBP and P/CAF, should facilitate the identification of other members of this AT family.