The Cdc13‐Stn1‐Ten1 complex stimulates Pol α activity by promoting the primase‐to‐polymerase switch (548.2)

Abstract

The Cdc13‐Stn1‐Ten1 complex stimulate Pol α activity by promoting the primase‐to‐polymerase switch Neal F. Lue1. 1Weill Medical College of Cornell University, New York, NY 10065 Emerging evidence suggests that Cdc13‐Stn1‐Ten1 (CST), an evolutionarily conserved RPA‐like ssDNA‐binding complex, may regulate Pol α activity at telomeres constitutively, and at other genomic locations under conditions of replication stress. However, the detailed mechanisms and the extent of evolutionary conservation are not understood. In this study, I examined the mechanisms of Pol α stimulation by CST using purified complexes derived from Candida glabrata. In the presence of physiologic concentrations of ribonucleotides and deoxyribonucleotides, CST did not enhance either the RNA primase or the DNA polymerase reaction, but rather augmented the efficiency of the primase‐to‐polymerase switch. In addition, CST simultaneously shortened the RNAs and lengthened the DNAs in the chimeric products synthesized by Pol α. Stn1, the most conserved subunit of CST, was alone capable of Pol α stimulation. Both the N‐terminal OB fold and the C‐terminal winged‐helix domains of Stn1 can separately bind the Pol12 subunit of the Pol α complex, and separately mediate Pol α activity enhancement. Overall, the findings suggest that Stn1 makes multiple, functionally important contacts with Pol12, causing an altered conformation of the Pol α‐primase complex capable of more efficient “handoff” of the RNA‐DNA hybrid from the primase to the polymerase. This mode of Pol α regulation has not been described before. Thus, the current report provides new mechanistic and evolutionary insights on a conserved pathway of Pol α regulation that is critical for genome stability.Grant Funding Source: NIH, NSF