Est1

ESt1, often written Est1 in yeast literature, is a non-catalytic component of the telomerase ribonucleoprotein (RNP) complex in budding yeast (Saccharomyces cerevisiae). It functions alongside the catalytic subunit Est2 and the RNA component TLC1 to maintain telomere length by promoting telomerase access and activity at chromosome ends.

Functionally, ESt1 binds to the telomere-associated protein Cdc13, helping recruit telomerase to telomeres. It also interacts with Est3 and Est2, forming part of the telomerase RNP that elongates telomeric DNA. ESt1 activity is tightly coordinated with the cell cycle, with recruitment to telomeres peaking in late S phase to align telomere synthesis with DNA replication.

Regulation and phenotype: Cells lacking ESt1 exhibit accelerated telomere shortening and enter a senescence-like state due to insufficient telomerase activity at telomeres. ESt1 levels and telomere association are controlled by cell cycle cues and telomere-binding networks, ensuring proper timing of telomere elongation.

Evolution and notes: Est1 homologs are present in a range of fungi and other eukaryotes, where they generally contribute to telomerase recruitment or regulation, though interaction partners and regulatory details vary across species. In Saccharomyces cerevisiae, the Est1–Cdc13 interaction is a central feature of telomerase targeting to chromosome ends.