Pol12, the B subunit of DNA polymerase α, functions in both telomere capping and length regulation

Abstract

The regulation of telomerase action, and its coordination with conventional DNA replication and chromosome end "capping," are still poorly understood. Here we describe a genetic screen in yeast for mutants with relaxed telomere length regulation, and the identification of Pol12, the B subunit of the DNA polymerase ␣ (Pol1)-primase complex, as a new factor involved in this process. Unlike many POL1 and POL12 mutations, which also cause telomere elongation, the pol12-216 mutation described here does not lead to either reduced Pol1 function, increased telomeric single-stranded DNA, or a reduction in telomeric gene silencing. Instead, and again unlike mutations affecting POL1, pol12-216 is lethal in combination with a mutation in the telomere end-binding and capping protein Stn1. Significantly, Pol12 and Stn1 interact in both two-hybrid and biochemical assays, and their synthetic-lethal interaction appears to be caused, at least in part, by a loss of telomere capping. These data reveal a novel function for Pol12 and a new connection between DNA polymerase ␣ and Stn1. We propose that Pol12, together with Stn1, plays a key role in linking telomerase action with the completion of lagging strand synthesis, and in a regulatory step required for telomere capping.

Unloading of homologous recombination factors is required for restoring double‐stranded DNA at damage repair loci

“…Recruitment of Polα to DNA and its activity which both rely on Polα interaction with RPA (Braun et al , 1997) might also depend on Rad51 removal by Srs2. During de novo telomere addition, the primase is expected to be recruited to the newly added TG repeats, perhaps via Pol12–Stn1 interaction (Grossi et al , 2004). It remains unclear whether Rad51 filaments would spread into the telomeric sequences or if Cdc13‐Stn1‐Ten1 would prevent the spreading.…”

Ten1p promotes the telomeric DNA-binding activity of Cdc13p: implication for its function in telomere length regulation

“…The fact that some ten1 mutants, including ten1-55 and ten1-66, exhibit longer telomeres supports this hypothesis. Since there exist interactions between Ten1p and Stn1p ( Figure 1B and 6B) npg [9,[23][24][25][26], Stn1p and Polα [25,30], as well as Cdc13p and Polα [19], another possibility could be that the interaction of Ten1p and Cdc13p tightens the binding of Cdc13p to telomeric G-strand to slow down the C-strand synthesis.…”

Replication of Telomeres and the Regulation of Telomerase

“…Importantly, the CST complex may play also an important role here, as physical interactions have been detected between Cdc13 and Pol1, the catalytic subunit of DNA Pol a-primase (Qi and Zakian 2000); and between Stn1 and Pol12, the B subunit of DNA Pol a-primase (Fig. 3) (Grossi et al 2004). Whether CST substitutes the related RPA stimulating the fill-in reaction is unknown.…”