The E1A-binding protein p300 is a histone acetyltransferase that also acts to acetylate other proteins, such as p53. p300 acts as a transcriptional coactivator that can serve as an adaptor molecule to bridge to transcriptional regulators. In addition, p300 binds to PCNA and may participate in chromatin remodeling.
The large p300 protein associates with CREB-binding protein(CBP) in numerous types of cells, forming the p300/CBP transcription co-activator that regulates gene expression by promoting acetylation of histones and other transcription factors, most notably p53. Dysregulation of the p300/CBP complex has been related to several types of human cancers.