Chromatin remodeling: a complex affair

ATP‐dependent chromatin remodelers are multi‐subunit enzymes that catalyze nucleosome dynamics essential for chromosomal functions, and their inactivation or dysregulation can lead to numerous diseases, including neuro‐degenerative disorders and cancers. Each remodeler contains a conserved ATPase “motor” whose activity or targeting can be regulated by enzyme‐specific, accessory subunits. The human ISWI subfamily of remodelers has been defined as a group of more than six different enzyme complexes where one of two related ATPase subunits (Snf2L/SMARCA1 and Snf2H/SMARCA5) is paired with one of six different accessory subunits. In this issue of EMBO Reports, Oppikofer et al 1 find that the human ISWI subfamily is even more polymorphic in nature—every known accessory subunit can interact and function with both ATPase isoforms. This raises the complexity of the human ISWI subfamily to > 12 distinct enzymes, with the possibility for much higher levels of combinatorial assemblies, and has the potential to create enzymes with novel biochemical activities, as well as novel regulatory wiring through differential interactions with locus‐specific factors or histone modifications.