In contrast to SRCAP, p400 is present in a complex together with the mammalian histone acetyltransferase TIP60 and about 16 other subunits, which together carry out functions in transcriptional regulation (particularly in transcriptional activation) and DNA damage repair (see ref. 85 for a review). There are no reports of mice that are null for components of the TIP60-p400 complex, except for TRRAP (homozygous Trrap-knockout embryos die at the peri-implantation stage)86. But in a recent RNAi screen for chromatin proteins that are required for mouse ESC self-renewal and pluripotency, Panning and colleagues found that reducing the protein levels of several components of the TIP60-p400 complex, including p400 and TIP60 themselves, resulted in premature differentiation and arrest of mouse ESCs87.
