Regulation of histone acetylation and transcription by INHAT, a human cellular complex containing the set oncoprotein

Acetylation of histones by p300/CBP and PCAF is considered to be a critical step in transcriptional regulation. In order to understand the role of cellular activities that modulate histone acetylation and transcription, we have purified and characterized a multiprotein cellular complex that potently inhibits the histone acetyltransferase activity of p300/CBP and PCAF. We have mapped a novel acetyltransferase-inhibitory domain of this INHAT (inhibitor of acetyltransferases) complex that binds to histones and masks them from being acetyltransferase substrates. Endogenous INHAT subunits, which include the Set/TAF-I beta oncoprotein, associate with chromatin in vivo and can block coactivator-mediated transcription when transfected in cells. We propose that histone masking by INHAT plays a regulatory role in chromatin modification and serves as a novel mechanism of transcriptional regulation.