Abstract
Dysfunctional telomere length regulation is detrimental to human health, and both activation and inhibition of telomerase have been proposed in potential therapies to treat human diseases. The Saccharomyces cerevisiae Pif1 protein is an evolutionarily conserved helicase that inhibits telomerase activity at DNA ends. Recent studies have indicated that Pif1 is specifically important for inhibiting telomerase at DNA ends with very little or no telomeric sequence and at long telomeres. At the former, Pif1 prevents the inappropriate addition of a telomere at DNA double-strand breaks. For the latter, Pif1 has been shown to bind long telomeres to presumably promote the extension of the short ones. These observations leave the impression that Pif1 does not act at DNA ends with telomeric sequence of intermediate length. Here, we provide in vivo evidence that Pif1 inhibits telomerase activity at DNA ends regardless of telomere sequence length.
Highlights
The ends of eukaryotic chromosomes are capped by telomeres, nucleoprotein complexes that protect chromosome ends from degradation, and telomere–telomere fusion (Ferreira et al 2004)
Telomere length homeostasis maintenance is a tightly regulated process and has been best studied in the budding yeast Saccharomyces cerevisiae, whose telomeres consist of 300 ± 75 bp of C1–3A/TG1–3 repeats (Wellinger and Zakian 2012)
The evidence suggests that Pif1 regulates telomere length by unwinding the DNA–RNA hybrid formed by the telomeric DNA and telomerase RNA subunit
Summary
The ends of eukaryotic chromosomes are capped by telomeres, nucleoprotein complexes that protect chromosome ends from degradation, and telomere–telomere fusion (Ferreira et al 2004). Pif1 function is important at double-strand DNA breaks (DSBs). Pif1 is thought to prevent telomere sequence addition at DSBs in cooperation with Mec1-dependent inhibition of the single-stranded telomeric DNA-binding protein Cdc13, which is needed for the recruitment of telomerase (Nugent et al 1996).
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