A basic motif anchoring ISWI to nucleosome acidic patch regulates nucleosome spacing

Recent studies have implicated the nucleosome acidic patch in the activity of ATP-dependent chromatin remodeling machines. We employed a photocrosslinking-based nucleosome profiling technology - ‘photoscanning’- to identify a conserved basic motif within the catalytic subunit of ISWI remodelers, SNF2h, which engages this nucleosomal epitope. This region of SNF2h is essential for chromatin remodeling activity in a reconstituted biochemical system and in cells. Our studies suggest that the basic motif in SNF2h plays a critical role in anchoring the remodeler to the nucleosomal surface. We also examine the functional consequences of several cancer-associated histone mutations that map to the nucleosome acidic patch. Kinetic studies employing physiologically relevant heterotypic nucleosomal substrates (‘Janus’ nucleosomes) indicate that these cancer mutations can disrupt regularly spaced chromatin structure by inducing ISWI-mediated unidirectional nucleosome sliding. These results imply a potential mechanistic link between oncogenic histones and alterations to the chromatin landscape.