In multicellular organisms, BAP or BAF complexes have enhanced abilities to bind histone modifications and hence might be guided by locus recognition, driven by specific histone modifications and regional architecture, rather than by simple sequence specificity or recruitment by transcription factors. The mammalian BAF (mSWI/SNF) and pBAF complexes collectively contain eight bromodomains (six on PBRM1, one on either BRG or BRM, and one on BRD7), two PHD finger proteins (BAF45 subunits), two chromodomains (BAF155 and BAF170), and between seven and nine DNA binding domains that can bind architectural features such as cruciform DNA structures, AT-rich sequences, or HMG recognition features (15–17, 19). Although a formal calculation of binding affinities has not been performed, the combined affinities would probably outweigh the binding energy provided by a transcription factor or even a group of them. An epigenetic locus recognition mechanism would provide a means by which complexes in multicellular organisms could be targeted to the loci with specific features determined by previous developmental events, and hence provide access to specific groups of genes bearing histone modifications that record their developmental history. In
