The CDC13-STN1-TEN1 complex stimulates Pol α activity by promoting RNA priming and primase-to-polymerase switch

Abstract

Emerging evidence suggests that Cdc13-Stn1-Ten1 (CST), an RPA-like ssDNA-binding complex, may regulate primase-Pol α (PP) activity at telomeres constitutively, and at other genomic locations under conditions of replication stress. Here we examine the mechanisms of PP stimulation by CST using purified complexes derived from Candida glabrata. While CST does not enhance isolated DNA polymerase activity, it substantially augments both primase activity and primase-to-polymerase switching. CST also simultaneously shortens the RNA and lengthens the DNA in the chimeric products. Stn1, the most conserved subunit of CST, is alone capable of PP stimulation. Both the N-terminal OB fold and the C-terminal winged-helix domains of Stn1 can bind to the Pol12 subunit of the PP complex, and stimulate PP activity. Our findings provide mechanistic insights on a well-conserved pathway of PP regulation that is critical for genome stability.

Regulating telomere length from the inside out: the replication fork model

“…A cocrystal shows binding of the Cdc13 N-terminal OB-fold domain to DNA polymerase α (Sun et al 2011). Stn1 and Ten1 in human cells were first identified as DNA polymerase α/primase accessory proteins (Goulian et al 1990), and biochemical reconstitution shows that the yeast t-RPA (CST) complex can stimulate DNA primase activity in vitro (Lue et al 2014), providing functional evidence for a role in DNA replication as well as telomere length regulation.…”

Dynamic Interactions of Arabidopsis TEN1: Stabilizing Telomeres in Response to Heat Stress

“…Cdc13 coordinates telomeric DNA replication by first facilitating G-strand synthesis through interactions with telomerase and then C-strand synthesis via association with DNA polymerase a/primase (Qi and Zakian, 2000). Unlike yeast CST, which stably and sequentially engages telomerase and DNA pol-a, vertebrate CST only transiently associates with telomeres, where it represses telomerase repeat addition processivity and stimulates Pol-a to facilitate the switch from G-strand to C-strand synthesis (Chen et al, 2012a;Lue et al, 2014). Vertebrate CST is also implicated in restoring replication fork progression following replication stress (Kasbek et al, 2013;Wang et al, 2012).…”

Control of telomerase action at human telomeres

“…However, this finding does not exclude the hypothesis that TIN2 DC mutations compromise telomerase-mediated telomere elongation as well 74 . Another tentative mechanism of telomerase regulation by shelterin is through the CTC1–STN1–TEN1 (CST) complex 75 , a stimulator of DNA polymerase α-primase (PαP) activity 76,77 . CST is recruited to the chromosome 3′ overhang at least in part by POT1 (Fig.…”