A chromodomain protein, Chp1, is required for the establishment of heterochromatin in fission yeast

Abstract

The chromodomain is a conserved motif that functions in the epigenetic control of gene expression. Here, we report the functional characterization of a chromodomain protein, Chp1, in the heterochromatin assembly in fission yeast. We show that Chp1 is a structural component of three heterochromatic regions-centromeres, the mating-type region, and telomeres-and that its localization in these regions is dependent on the histone methyltransferase Clr4. Although deletion of the chp1 þ gene causes centromerespecific decreases in Swi6 localization and histone H3-K9 methylation, we show that the role of Chp1 is not exclusive to the centromeres. We found that some methylation persists in native centromeric regions in the absence of Chp1, which is also true for the mating-type region and telomeres, and determined that Swi6 and Chp2 are critical to maintaining this residual methylation. We also show that Chp1 participates in the establishment of repressive chromatin in all three chromosomal regions. These results suggest that different heterochromatic regions share common structural properties, and that centromeric heterochromatin requires Chp1-mediated establishment steps differently than do other heterochromatic regions.

Elimination of shelterin components bypasses RNAi for pericentric heterochromatin assembly

“…3C; Sadaie et al 2004). The histone deacetylases Clr3 and Sir2 function cooperatively with RNAi to establish heterochromatin at pericentric repeats, and H3K9me2 is completely abolished in clr3D dcr1D and sir2D dcr1D cells (Yamada et al 2005;Alper et al 2013;Buscaino et al 2013;Marina et al 2013).…”

“…RNAi is required for both the establishment and maintenance of heterochromatin at pericentric regions (Sadaie et al 2004). To distinguish whether poz1D dcr1D rescues heterochromatin maintenance or establishment, we introduced otrTura4 + in either a silenced state (from wildtype cells) or a desilenced state (from clr4D cells) into poz1D dcr1D cells by genetic crosses (Fig.…”

“…As a result, loss of RNAi severely affects pericentric heterochromatin functions but has little effect on heterochromatin structures at the silent mating type region or telomeres. However, even at pericentric regions, H3K9me and Swi6 are still present in RNAi mutants, albeit at lower levels, suggesting the existence of RNAi-independent mechanisms to establish heterochromatin (Sadaie et al 2004). These pathways involve the Clr3 and Sir2 histone deacetylases since H3K9me levels are further reduced from pericentric regions in clr3D dcr1D and sir2D dcr1D cells, although Sir2 seems to function in a separate pathway from Clr3 (Yamada et al 2005;Alper et al 2013;Buscaino et al 2013;Marina et al 2013).…”

RNAs — Physical and functional modulators of chromatin reader proteins

“…Interestingly, this organism does not have any Pc like factors. The chromodomains of both, Chp1 and Clr4 specifically interact with methyl-H3K9 [43][44][45]. While Chp1 is a part of the RNAi-induced transcriptional silencing (RITS) complex whose core subunits consist of Argonaute, Tas3 and Chp1, Clr4 is a H3K9-specific methyltransferase (HMTase).…”

“…While Chp1 is a part of the RNAi-induced transcriptional silencing (RITS) complex whose core subunits consist of Argonaute, Tas3 and Chp1, Clr4 is a H3K9-specific methyltransferase (HMTase). Both proteins play pivotal roles in the RNAi pathway and in heterochromatin-mediated gene silencing in yeast (reviewed in [30], [43,46]). For both Chp1 and Clr4, the interaction with RNA is partly mediated by a stretch of 5-6 basic amino acids located at the C-terminus of the α-helix within their chromodomains (Fig.…”