The SWI/SNF family of complexes, which are conserved from yeast to humans, are ATP-dependent chromatin-remodelling proteins that facilitate transcription activation . The mammalian complexes are made up of 9-12 proteins called BAFs (BRG1-associated factors). The BAF60 family have at least three members: BAF60a, which is ubiquitous, BAF60b and BAF60c, which are expressed in muscle and pancreatic tissues, respectively. BAF60b is present in alternative forms of the SWI/SNF complex, including complex B (SWIB), which lacks BAF60a. The SWIB domain is a conserved region found within the BAF60b proteins , and can be found fused to the C-terminus of DNA topoisomerase in Chlamydia.
MDM2 is an oncoprotein that acts as a cellular inhibitor of the p53 tumour suppressor by binding to the transactivation domain of p53 and suppressing its ability to activate transcription . p53 acts in response to DNA damage, inducing cell cycle arrest and apoptosis. Inactivation of p53 is a common occurrence in neoplastic transformations. The core of MDM2 folds into an open bundle of four helices, which is capped by two small 3-stranded beta-sheets. It consists of a duplication of two structural repeats. MDM2 has a deep hydrophobic cleft on which the p53 alpha-helix binds; p53 residues involved in transactivation are buried deep within the cleft of MDM2, thereby concealing the p53 transactivation domain.
The SWIB and MDM2 domains are homologous and share a common fold.