FIG 7.

Cdk1 regulates the recruitment of telomerase complex and CST complex to the telomere during cell cycle progression. During the S phase, only a small fraction of telomeres are elongated. Phosphorylation of Cdc13 by Cdk1 results in the preferential recruitment of telomerase complexes to the telomeres. The subsequent phosphorylation of Stn1 by Cdk1 results in the stable formation of Cdc13-Stn1-Ten1 (CST) complex. On the one hand, the binding of CST complex is necessary to protect the telomeres that are not elongated by telomerase complexes from being further processed by the nucleases; on the other hand, the CST complex is necessary to inhibit the telomere elongation by telomerase. Thus, the cell cycle-dependent phosphorylations of Cdc13 and Stn1 by Cdk1 regulate the recruitment of telomerase complexes and CST complexes to the telomeres.