title: Proteasome-dependent degradation of Est1p regulates the cell cycle-restricted assembly of telomerase in Saccharomyces cerevisiae.
abstract: Telomerase counteracts loss of terminal sequences incurred during DNA replication. In S. cerevisiae, telomerase contains an RNA template (TLC1), a reverse transcriptase (Est2p) and at least two regulatory proteins (Est1p and Est3p). Whereas Est2p is constitutively telomere bound, Est1p associates in late S phase, coincident with telomere lengthening. Here we directly demonstrate by coimmunoprecipitation that the composition of telomerase varies during the cell cycle. The absence of Est1p and Est3p from the complex during G1 phase can be attributed to proteasome-dependent degradation of Est1p. Stabilization of Est1p during G1 phase promotes telomerase assembly, revealing a previously uncharacterized role for Est1p in the recruitment of Est3p to the telomerase complex. Though catalytically active, complexes assembled during G1 cannot lengthen telomeres. We conclude that telomerase assembly during G1 phase is regulated by Est1p stability, but assembly is insufficient to activate telomerase at telomeres.
authors.affiliation: Department of Biological Sciences, Vanderbilt University, VU Station B 351634, Nashville, Tennessee 37235, USA.
authors.forename: Jennifer L
authors.initials: JL
authors.lastname: Osterhage
authors.forename: Jennell M
authors.initials: JM
authors.lastname: Talley
authors.forename: Katherine L
authors.initials: KL
authors.lastname: Friedman
mesh_terms: D002453:Cell Cycle / Q000502:physiology*; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism; D016193:G1 Phase / Q000502:physiology; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism*; D012441:Saccharomyces cerevisiae / Q000166:cytology / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins / Q000235:genetics / Q000378:metabolism*; D019098:Telomerase / Q000235:genetics / Q000378:metabolism*
chemical_list: D004268:DNA-Binding Proteins; D029701:Saccharomyces cerevisiae Proteins; C099024:EST1 protein, S cerevisiae; C491580:EST3 protein, S cerevisiae; D019098:Telomerase; D046988:Proteasome Endopeptidase Complex