Title

Inhibition of Yeast Telomerase Action by the Telomeric ssDNA-binding Protein, Cdc13p

Document Type

Article

Publication Date

Fall 11-29-2008

Publication Title

Nucleic Acids Research

Volume

37

Issue

2

First Page

354

Last Page

367

DOI

10.1093/nar/gkn830

Abstract

Appropriate control of the chromosome end-replicating enzyme telomerase is crucial for maintaining telomere length and genomic stability. The essential telomeric DNA-binding protein Cdc13p both positively and negatively regulates telomere length in budding yeast. Here we test the effect of purified Cdc13p on telomerase action in vitro. We show that the full-length protein and its DNA-binding domain (DBD) inhibit primer extension by telomerase. This inhibition occurs by competitive blocking of telomerase access to DNA. To further understand the requirements for productive telomerase 3′-end access when Cdc13p or the DBD is bound to a telomerase substrate, we constrained protein binding at various distances from the 3′-end on two sets of increasingly longer oligonucleotides. We find that Cdc13p inhibits the action of telomerase through three distinct biochemical modes, including inhibiting telomerase even when a significant tail is available, representing a novel ‘action at a distance’ inhibitory activity. Thus, while yeast Cdc13p exhibits the same general activity as human POT1, providing an off switch for telomerase when bound near the 3′-end, there are significant mechanistic differences in the ways telomere end-binding proteins inhibit telomerase action.

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