The Paf1 complex factors Leo1 and Paf1 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 Schizosaccharomyces pombe and monitored the silencing of reporter genes inserted into the euchromatic region adjacent to the heterochromatic mating type locus. We show that Leo1-Paf1 [a subcomplex of the RNA polymerase II-associated factor 1 complex (Paf1C)] is required to prevent the spreading of heterochromatin into euchromatin by mapping the heterochromatin mark H3K9me2 using high-resolution genomewide ChIP (ChIP-exo). Loss of Leo1-Paf1 increases heterochromatin stability at several facultative heterochromatin loci in an manner. Instead, deletion of Leo1 decreases nucleosome turnover, leading to heterochromatin stabilization. Our data reveal that Leo1-Paf1 promotes chromatin state fluctuations by enhancing histone turnover.

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