Rsc1 DNA-binding bromodomain drives RSC activity at A-rich promoters

In yeast, the SWI/SNF chromatin remodeler RSC orchestrates nucleosome positioning at promoters, yet the molecular determinants guiding RSC to chromatin remain unclear. Here, we investigate the RSC subunit Rsc1 in Candida albicans and Saccharomyces cerevisiae. We identify a non-canonical role for its second bromodomain, Rsc1-BD2, which lacks a functional acetyllysine-binding pocket. Instead, Rsc1-BD2, together with the adjacent AT-hook and BAH domains, forms a conserved DNA-binding surface that is critical for RSC-dependent nucleosome remodeling and essential for viability in both species. Genome-wide motif analysis reveals that promoter regions are enriched in polyA sequences, whose distribution correlates with nucleosome positioning and gene expression. We show that Rsc1 preferentially binds polyA motifs and that nucleosome positioning at polyA-rich promoters depends on Rsc1 DNA binding module. These findings establish Rsc1 as a sequence-specific DNA-binding factor that mediates RSC stimulation by polyA motifs at yeast promoters. Overall, this study expands our understanding of the functional diversity of bromodomains and provides insights into the mechanisms governing RSC targeting to chromatin.