ASH-1-catalyzed H3K36 methylation drives gene repression and marks H3K27me2/3-competent chromatin

ASH-1 orthologs are H3K36-specific methyltransferases that are conserved from fungi to humans but are poorly understood, in part because they are typically essential for viability. Here we examine the H3K36 methylation pathway of Neurospora crassa, which we find has just two H3K36 methyltransferases, ASH-1 and RNA polymerase II-associated SET-2. Our investigation of the interplay between SET-2 and ASH-1 uncovered a regulatory mechanism connecting ASH-1-catalyzed H3K36 methylation to repression of poorly transcribed genes. Our findings provide new insight into ASH-1 function, H3K27me2/3 establishment, and repression at facultative heterochromatin. RNA-seq: We analyzed gene expression changes in Neurospora crassa by poly-A+ mRNA-sequencing performed in duplicate. A wild type strain (N3752) serves as the reference strain (deposited in GSE82222). ChIP-seq: We analyzed the distribution of histone H3 lysine 27 methylation (H3K27me2/3), H3K36me2/3, and H3K27ac in Neurospora crassa by chromatin immunoprecipitation. Strains were grown, crosslinked, lysed, modified nucleosomes were immunopurified, and associated DNA was sequenced.