However, through 500 million years of evolution, several subunits, which are remnants of the yeast SWI/SNF complex remain constant. First is the structure of the ATPase subunit and the so-called helicase domains of Brg and Brm, which show a remarkable degree of conservation between them, as with all of the 29 members of this family of chromatin remodeling complexes. This suggests that fundamental mechanisms are conserved among the entire group of SWI2-like remodelers. In addition, the BAF155 and BAF170 subunits are clearly homologs of SWI3, BAF47 is clearly a homolog of SNF5, and SWP73 is a homolog of BAF60. Whereas the mammalian and Drosophila complexes contain β-actin, actin is only found in the INO80 and SWR1 complexes and not in the yeast SWI/SNF or RSC complexes (21–23). The yeast SWI/SNF complex has two Arp subunits; however, they do not polymerize, nor do they have ATPase activity. In contrast, β-actin has both of these critical activities. Thus, in this respect, mammalian BAF complexes resemble yeast INO80 and SWR1, which play critical roles as guardians of the genome against the accumulation of mutations (24) and are probably most analogous to the p53 function in vertebrates.
