Hsk1–Dfp1 is required for heterochromatin-mediated cohesion at centromeres

Abstract

Heterochromatin performs a central role in chromosome segregation and stability by promoting cohesion at centromeres. Establishment of both heterochromatin-mediated silencing and cohesion requires passage through S phase, although the mechanism is unknown. Here we demonstrate that Schizosaccharomyces pombe Hsk1 (CDC7), a conserved Dbf4-dependent protein kinase (DDK) that regulates replication initiation, interacts with and phosphorylates the heterochromatin protein 1 (HP1) equivalent Swi6 (ref. 6). Hsk1 and its regulatory subunit Dfp1 function downstream of Swi6 localization to promote heterochromatin function and cohesion specifically at centromeres. This role for Hsk1-Dfp1 is separable from its replication initiation activity, providing a temporal link between S phase and centromere cohesion that is mediated by heterochromatin.

Diverse roles of HP1 proteins in heterochromatin assembly and functions in fission yeast

“…We also identified peptides, albeit few, corresponding to previously described Swi6-associated proteins, such as JmjC protein Epe1 (38, 39), Hsk1-Dfp1 (40,41), and Pcr1 involved in heterochromatic silencing (42). Also detected were peptides representing different subunits of SHREC (Fig.…”

Interaction of APC/C-E3 Ligase with Swi6/HP1 and Clr4/Suv39 in Heterochromatin Assembly in Fission Yeast

“…Recently, Hsk1-Dfp1-mediated phosphorylation of Swi6 has been shown to be critical for stabilizing the binding of Swi6 to heterochromatin (7). Phosphorylation causes a reduction in the electrophoretic mobility of Swi6 (7).…”

“…Further work has shown that the RNAi pathway plays a role in the establishment of heterochromatin but not for its spreading (4). The binding of Swi6 is also regulated through phosphorylation by the Hsk1-Dfp1 complex (7); mutations in the Hsk1-Dfp1 kinase complex reduce the binding of Swi6 to heterochromatin, leading to the loss of silencing, increased chromosomal segregation defects, and chromosomal loss during mitosis (7).…”

Symmetry, asymmetry, and kinetics of silencing establishment in Saccharomyces cerevisiae revealed by single-cell optical assays

“…W303-derived yeast strains containing the hml::pURA3:: GFP::PEST::NLS were generated from Yex730 (23). The original Yex730 strain was created by cloning the first 55 amino acids of the CLN2 PEST degradation tag onto the carboxy-terminal end of yEGFP (Clontech) (40,48). This construct was transformed into a plasmid to produce the fusion gene URA3promoter::NLS::EGFP::PEST::URA3 terminator.…”