The pBAF complex was discovered by biochemical purification of proteins required for ligand-activated transcription in vitro (91). The name pBAF came from the discovery that this complex contained polybromo (PBRM1 or BAF180) and BAF200 (Arid2), as well as Brg (but not Brm) and several other subunits of the BAF complex. The BAF180 protein contains six bromodomains that are similar to the single bromodomain found in Brg1. BAF180 is mutated or deleted in more than 50% of clear cell renal cell carcinoma (ccRCC) (92). Here again, the tumors do not occur in childhood, and to date, there are no specific pathologic features of this tumor subgroup. Although a number of alleles are predicted not to produce protein, many of the missense mutations occur in the bromodomains. It seems that the bromodomains are not redundant for the tumor suppressor function in that mutation of any single bromodomain in one allele is sufficient to contribute to cancer formation. We assume that the bromodomains bind to acetylated histones, and they do indeed do this in vitro, but their in vivo binding specificity has not yet been determined.
