The P af1 complex factors L eo1 and P af1 promote local histone turnover to modulate chromatin states in fission yeast

The maintenance of open and repressed chromatin states is crucial for the regulation of gene expression. To study the genes involved in maintaining chromatin states, we generated a random mutant library in S chizosaccharomyces pombe and monitored the silencing of reporter genes inserted into the euchromatic region adjacent to the heterochromatic mating type locus. We show that L eo1– P af1 [a subcomplex of the RNA polymerase II ‐associated factor 1 complex ( P af1 C )] is required to prevent the spreading of heterochromatin into euchromatin by mapping the heterochromatin mark H 3 K 9me2 using high‐resolution genomewide C h IP ( C h IP –exo). Loss of L eo1– P af1 increases heterochromatin stability at several facultative heterochromatin loci in an RNA i‐independent manner. Instead, deletion of L eo1 decreases nucleosome turnover, leading to heterochromatin stabilization. Our data reveal that L eo1– P af1 promotes chromatin state fluctuations by enhancing histone turnover.