The nucleolar protein Nsk1 modulates rDNA silencing during interphase.

Nsk1 acts at kinetochores during mitosis to prevent error-prone chromosome segregation and it is phosphoregulated by Cdk1 . The Clp1 / Cdc14 protein phosphatase, to which Nsk1 binds, reverses Cdk1-mediated phosphorylation of Nsk1 during anaphase. During interphase, Nsk1 localizes exclusively to the nucleolus and its function there is unknown. In this study, we examined whether Nsk1 shares functions in the nucleolus with other known Clp1 / Cdc14 phosphatase substrates that localize there. We found that Nsk1 participates in rRNA silencing but not rDNA segregation, rDNA transcription, or nucleolar organization.