P300 CREB BINDING PROTEIN-RELATED PROTEIN P270 IS A COMPONENT OF MAMMALIAN SWI/SNF COMPLEXES/

p300 and the closely related CREB binding protein (CBP) are transcript ional adaptors that are present in intracellular complexes with TATA b inding protein (TBP) and bind to upstream activators including p53 and nuclear hormone receptors. They have intrinsic and associated histone acetyltransferase activity, suggesting that chromatin modification is an essential part of their role in regulating transcription. Detailed characterization of a panel of antibodies raised against p300/CBP has revealed the existence of a 270-kDa cellular protein, p270, distinct from p300 and CBP but sharing at least two independent epitopes with p 300. The subset of p300/CBP-derived antibodies that cross-reacts with p270 consistently coprecipitates a series a cellular proteins with rel ative molecular masses ranging from 44 to 190 kDa. Purification and an alysis of various proteins in this group reveals that they are compone nts of the human SWI/SNF complex and that p270 is an integral member o f this complex.