Rapid turnover of the tumor suppressor protein p53 requires the MDM2 ubiquitin ligase, and both interact with p300-CREB-binding protein transcriptional coactivator proteins. p53 is stabilized by the binding of p300 to the oncoprotein E1A, suggesting that p300 regulates p53 degradation. Purified p300 exhibited intrinsic ubiquitin ligase activity that was inhibited by E1A. In vitro, p300 with MDM2 catalyzed p53 polyubiquitination, whereas MDM2 catalyzed p53 monoubiquitination. E1A expression caused a decrease in polyubiquitinated but not monoubiquitinated p53 in cells. Thus, generation of the polyubiquitinated forms of p53 that are targeted for proteasome degradation requires the intrinsic ubiquitin ligase activities of MDM2 and p300.
SciCrunch is a data sharing and display platform. Anyone can create a custom portal where they can select searchable subsets of hundreds of data sources, brand their web pages and create their community. SciCrunch will push data updates automatically to all portals on a weekly basis. User communities can also add their own data to scicrunch, however this is not currently a free service.