ATP-dependent remodeling of chromatin condensates reveals distinct mesoscale outcomes

ATP-dependent chromatin remodeling enzymes mobilize nucleosomes, but how such mobilization affects chromatin condensation is unclear. Here, we investigate effects of two major remodelers, ACF and RSC using chromatin condensates and single-molecule footprinting. We find that both remodelers inhibit the formation of condensed chromatin. However, the remodelers have distinct effects on pre-formed chromatin condensates. ACF spaces nucleosomes without de-condensing the chromatin, explaining how ACF maintains nucleosome organization in transcriptionally repressed genomic regions. In contrast, RSC catalyzes ATP-dependent de-condensation of chromatin. RSC also drives micron-scale movements of entire chromatin condensates. These additional activities of RSC may contribute to its central role in transcription. The biological importance of remodelers may thus reflect both their effects on nucleosome mobilization and the corresponding consequences on chromatin dynamics at the mesoscale. Chromatin was assembled in vitro via salt gradient dialysis. Chromatin arrays were remodeled in vitro with ATP-dependent chromatin remodelers and visualized via microscopy. Chromatin was then profiled with m6A methyltransferase footprinting and SMRT long-read sequencing (SAMOSA-ChAAT). 36 in vitro chromatin samples were analyzed.