to untangle DNA at anaphase, whereas deletion of non-oncogenic subunits did not have this effect (97). The deletion of oncogenic BAF subunits surprisingly leads to arrest at G2/M with high levels of histone H3 S-10 phosphorylation, an indicator of incomplete mitosis. The deletion of the oncogenic subunits gives rise to the decatenation checkpoint, which arrests cells until the tangled DNA can be decatenated. Consistent with this, the arrest can be overcome by a mutation in TopoIIa, which prevents its phosphorylation and the sensing mechanism that tells the cell that its DNA is tangled. BAF complexes bind robustly to endogenous TopoII, and peptides from TopoII have been recovered in each of five different proteomic analysis of endogenous, untagged BAF complexes from different tissues. The role of BAF seems to allow TopoII to bind to DNA. TopoII’s interaction with DNA is so transient that it is difficult to detect by ordinary Chip-seq. However, by arresting the progression of the mechanism of TopoII using etoposide, it was possible to capture the enzyme covalently attached to DNA before the religation step could be completed. Using this approach, the Brg (Smarca4) ATPase was found to be essential for the binding of TopoII to 11,000 of
