SRA

The classic view of nucleosome organization at active promoters is that two well-positioned nucleosomes flank a nucleosome-depleted region (NDR). However, this view has been recently challenged by contradictory reports as to whether a distinct set of wider (?150 bp) NDRs instead contain unusually unstable Micrococcal Nuclease-sensitive “fragile” particles, thought to be nucleosomal because of their size. To determine the composition of fragile particles we introduce CUT&RUN.ChIP, in which targeted nuclease cleavage and release is followed by chromatin immunoprecipitation. We find that fragile particles represent the occupancy and action of the RSC nucleosome remodeler acting on dynamically unwrapped nucleosomal intermediates. We also find that general regulatory factors (GRFs) bind to partially unwrapped nucleosomal intermediates at NDRs. We propose that RSC-engagement and its action cause nucleosomes to unravel, and subsequent binding of GRFs constitute a dynamic cycle of nucleosome deposition and clearance at the subset of wide Pol II promoter NDRs. Overall design: We used Cleavage under targets and Release using nuclease (Cut-and-Run), a chromatin profiling strategy in which antibody-targeted controlled cleavage by micrococcal nuclease releases specific protein-DNA complexes into the supernatant for paired-end DNA sequencing, followed by chromatin immunoprecipitation (ChIP).