H2BC21 and cancer: Tip60-p400 has been purified from cancer cell lines as a 17 subunit chromatin remodeling complex with two chromatin remodeling activities: the Tip60 (also known as Kat5) subunit acetylates the N-terminal tails of histones H2A, H4, and a number of transcription factors, while the p400 subunit mediates exchange of H2A–H2B dimers for H2AZ–H2B dimers within nucleosomes (Doyon et al., 2004; Cai et al., 2005; Squatrito et al., 2006).