The Saccharomyces telomere-binding protein Cdc13p interacts with both the catalytic subunit of DNA polymerase α and the telomerase-associated Est1 protein

Saccharomyces telomeres consist of -350 bp of C_1-3A/TG_1-3 DNA. Most of this -350 bp is replicated by standard, semiconservative DNA replication. After conventional replication, the C_1-3A strand is degraded to generate a long single strand TG_1-3 tail that can serve as a substrate for telomerase. Cdc13p is a single strand TG_1-3 DNA-binding protein that localizes to telomeres in vivo. Genetic data suggest that the Cdc13p has multiple roles in telomere replication. We used two hybrid analysis to demonstrate that Cdc13p interacted with both the catalytic subunit of DNA polymerase α, Pol1p, and the telomerase RNA-associated protein, Est1p. The association of these proteins was confirmed by biochemical analysis using full-length or nearly full-length proteins. Point mutations in either CDC13 or POL1 that reduced the Cdc13p-Pol1p interaction resulted in telomerase mediated telomere lengthening. Over-expression of the carboxyl terminus of Est1p partially suppressed the temperature sensitive lethality of a cdc13-1 strain. We propose that Cdc13p's interaction with Est1p promotes TG_1-3 strand lengthening by telomerase and its interaction with Pol1p promotes C_1-3A strand resynthesis by DNA polymerase α.