SWR-C and INO80 chromatin remodelers recognize nucleosome-free regions near +1 nucleosomes

Abstract

SWR-C/SWR1 and INO80 are multisubunit complexes that catalyze the deposition and removal, respectively, of histone variant H2A.Z from the first nucleosome at the start of genes. How they target and engage these +1 nucleosomes is unclear. Using ChIP-exo, we identified the subnucleosomal placement of 20 of their subunits across the yeast genome. The Swc2 subunit of SWR-C bound a narrowly defined region in the adjacent nucleosome-free region (NFR), where it positioned the Swr1 subunit over one of two sites of H2A.Z deposition at +1. The genomic binding maps suggest that many subunits have a rather plastic organization that allows subunits to exchange between the two complexes. One outcome of promoting H2A/H2A.Z exchange was an enhanced turnover of entire nucleosomes, thereby creating dynamic chromatin at the start of genes. Our findings provide unifying concepts on how these two opposing chromatin remodeling complexes function selectively at the +1 nucleosome of nearly all genes.