Drosophila BAF complex crosslinking (

Mammalian SWI/SNF (mSWI/SNF) ATP-dependent chromatin remodeling complexes are large, multisubunit molecular machines that play vital roles in regulating genomic architecture and are frequently disrupted in human cancer and developmental disorders. To date, the organization and pathway of assembly of these chromatin regulators remain unknown, presenting a major barrier to structural and functional determination. Here we elucidate the architecture and assembly pathway of three different classes of mammalian SWI/SNF complexes: canonical BAF, PBAF, and a newly defined complex, ncBAF, and define the requirement of each subunit for complex formation and stability. Using affinity purification of endogenous complexes from mammalian and Drosophila cells coupled with cross linking-mass spectrometry, we uncover three distinct and evolutionarily conserved modules, their organization, and the temporal incorporation of these modules into each complete mSWI/SNF complex class.