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

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Abstract
Heterochromatin performs a central role in chromosome segregation and stability by promoting cohesion at centromeres1,2. Establishment of both heterochromatin-mediated silencing and cohesion requires passage through S phase, although the mechanism is unknown3,4. Here we demonstrate that Schizosaccharomyces pombe Hsk1 (CDC7), a conserved Dbf4-dependent protein kinase (DDK) that regulates replication initiation5, 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.