ATPase Brg1 (Smarca4) of BAF complexes leads to H3K27Me3 accumulation and repression of many genes in embryonic stem (ES) cells (11). Additional evidence that BAF opposes Polycomb has come from studies of human malignancy, as will be discussed below (see “BAF Complexes as Tumor Suppressors: Key Mechanistic Themes”). However, genes with related functions (such as to oppose Polycomb-mediated repression) were also discovered in histone modification genes, notably in the MLL genes that are subunits of the COMPASS complex and provide the activating modification H3K4Me3 (2, 12).
