title: The Est1 subunit of Saccharomyces cerevisiae telomerase makes multiple contributions to telomere length maintenance.
abstract: The telomerase-associated Est1 protein of Saccharomyces cerevisiae mediates enzyme access by bridging the interaction between the catalytic core of telomerase and the telomere-binding protein Cdc13. In addition to recruiting telomerase, Est1 may act as a positive regulator of telomerase once the enzyme has been brought to the telomere, as previously suggested by the inability of a Cdc13-Est2 fusion protein to promote extensive telomere elongation in an est1-Delta strain. We report here three classes of mutant Est1 proteins that retain association with the telomerase enzyme but confer different in vivo consequences. Class 1 mutants display a telomere replication defect but are capable of promoting extensive telomere elongation in the presence of a Cdc13-Est2 fusion protein, consistent with a defect in telomerase recruitment. Class 2 mutants fail to elongate telomeres even in the presence of the Cdc13-Est2 fusion, which is the phenotype predicted for a defect in the proposed second regulatory function of EST1. A third class of mutants impairs an activity of Est1 that is potentially required for the Ku-mediated pathway of telomere length maintenance. The isolation of mutations that perturb separate functions of Est1 demonstrates that a telomerase holoenzyme subunit can contribute multiple regulatory roles to telomere length maintenance.
authors.affiliation: Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, Texas 77030, USA.
authors.forename: Sara K
authors.initials: SK
authors.lastname: Evans
authors.forename: Victoria
authors.initials: V
authors.lastname: Lundblad
mesh_terms: D000595:Amino Acid Sequence; D024342:Amino Acids, Acidic; D024361:Amino Acids, Basic; D017124:Conserved Sequence; D004252:DNA Mutational Analysis; D015966:Gene Expression Regulation, Fungal; D016297:Mutagenesis, Site-Directed; D020125:Mutation, Missense; D012441:Saccharomyces cerevisiae / Q000235:genetics / Q000378:metabolism; D029701:Saccharomyces cerevisiae Proteins / Q000235:genetics* / Q000378:metabolism*; D016415:Sequence Alignment; D019098:Telomerase / Q000235:genetics* / Q000378:metabolism*; D016615:Telomere / Q000235:genetics*; D034501:Telomere-Binding Proteins / Q000378:metabolism
chemical_list: D024342:Amino Acids, Acidic; D024361:Amino Acids, Basic; C452219:Cdc13 protein, S cerevisiae; D029701:Saccharomyces cerevisiae Proteins; D034501:Telomere-Binding Proteins; C099024:EST1 protein, S cerevisiae; D019098:Telomerase