Polycomb Repressive Complex 2 (PRC2) is a conserved epigenetic regulator that represses gene expression through methylation of histone H3 lysine 27 (H3K27me3). In animals, plants, and some fungi, PRC2-directed facultative heterochromatin plays essential roles in development and cellular differentiation. Here, we show that the replication-dependent histone chaperone Chromatin Assembly Factor 1 (CAF-1) is required for proper structure and function of facultative heterochromatin in the model fungus Neurospora crassa. Loss of CAF-1 causes widespread transcriptional misregulation, particularly within PRC2-repressed regions, and leads to redistribution of H3K27me3, reduced ASH1-dependent H3K36 methylation, and accumulation of chromatin marks associated with active transcription. CAF-1 was not required for repressive histone methylation within constitutive heterochromatin. A double mutant lacking both CAF-1 and PRC2 components displayed a synergistic silencing defect, suggesting these complexes make distinct contributions to facultative heterochromatin. Together, our findings indicate that CAF-1 works in concert with PRC2 to silence transcription within N. crassa facultative heterochromatin domains.
Lewis, Z. A., Torres, E. V., Yap, R. E., Ferraro, A. R., Link, C. D., Pelham, J. F.
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