The 2-megadalton mammalian BAF complexes consist of at least 15 subunits, five of which have homologs in the yeast SWI/SNF (BRG1/BRM, BAF155/170, BAF60, BAF53, BAF47) (Figure 1, Table I). However, the mamm alian BAF has diverged significantly from the yeast counterpart, losing some subunits while gaining novel core subunit families including BAF250a/b (ARID1a/b), BAF45a/b/c/d, BAF57, β-actin, BRD7, BRD9 and SS18/CREST; of note, BAF250a/b are the most frequently mutated BAF subunits in human malignancy and neurological disorders (Ho et al., 2009b; Kadoch et al., 2013). Furthermore, while the yeast SWI/SNF has an exclusively activating role, BAF complexes can both activate or repress their genomic targets (Boyer et al., 2005; Ho et al., 2009a, 2011). Thus, the mammalian BAF complexes only have limited similarities with the yeast SWI/SNF complex. The changes in subunit composition correspond to the emergence of multicellularity, and even later changes correspond to the development of complex nervous systems; the later evolutionary point is reflected in their frequent implication in neurologic disease.
