Cdc6 is sequentially regulated by PP2A-Cdc55, Cdc14, and Sic1 for origin licensing in S. cerevisiae

• DOI: 10.7554/elife.74437
• Publication Date: 2022-02-10T02:00:16Z
• Authors: Jasmin Philip; Mihkel Örd; Andriele Silva; Shaneen Singh; John FX Diffley; Dirk Remus; Mart Loog; Amy E Ikui
• Keywords: DNA Replication; Model organisms; 0301 basic medicine; Saccharomyces cerevisiae Proteins; QH301-705.5; Science; Mitosis; Cell Cycle Proteins; Saccharomyces cerevisiae; DNA replication; Cdc6; Biochemistry & Proteomics; phosphatase; 03 medical and health sciences; Protein Phosphatase 2; Biology (General); Phosphorylation; Cyclin-Dependent Kinase Inhibitor Proteins; 0303 health sciences; Q; Genome Integrity & Repair; R; Cell Biology; PP2A; Cdc14; Cdc55; Medicine; Cell Cycle & Chromosomes; Protein Tyrosine Phosphatases; Genetics & Genomics; Structural Biology & Biophysics

Cdc6, a subunit of the pre-replicative complex (pre-RC), contains multiple regulatory cyclin-dependent kinase (Cdk1) consensus sites, SP or TP motifs. In Saccharomyces cerevisiae, Cdk1 phosphorylates Cdc6-T7 to recruit Cks1, the Cdk1 phospho-adaptor in S phase, for subsequent multisite phosphorylation and protein degradation. Cdc6 accumulates in mitosis and is tightly bound by Clb2 through N-terminal phosphorylation in order to prevent premature origin licensing and degradation. It has been extensively studied how Cdc6 phosphorylation is regulated by the cyclin–Cdk1 complex. However, a detailed mechanism on how Cdc6 phosphorylation is reversed by phosphatases has not been elucidated. Here, we show that PP2ACdc55 dephosphorylates Cdc6 N-terminal sites to release Clb2. Cdc14 dephosphorylates the C-terminal phospho-degron, leading to Cdc6 stabilization in mitosis. In addition, Cdk1 inhibitor Sic1 releases Clb2·Cdk1·Cks1 from Cdc6 to load Mcm2–7 on the chromatin upon mitotic exit. Thus, pre-RC assembly and origin licensing are promoted by phosphatases through the attenuation of distinct Cdk1-dependent Cdc6 inhibitory mechanisms.