title: Distinct requirements for Pot1 in limiting telomere length and maintaining chromosome stability.
abstract: The fission yeast Pot1 (protection of telomeres) protein binds to the single-stranded extensions at the ends of telomeres, where its presence is critical for the maintenance of linear chromosomes. Homologs of Pot1 have been identified in a wide variety of eukaryotes, including plants, animals, and humans. We now show that Pot1 plays dual roles in telomere length regulation and chromosome end protection. Using a series of Pot1 truncation mutants, we have defined distinct areas of the protein required for chromosome stability and for limiting access to telomere ends by telomerase. We provide evidence that a large portion of Pot1, including the N-terminal DNA binding domain and amino acids close to the C terminus, is essential for its protective function. C-terminal Pot1 fragments were found to exert a dominant-negative effect by displacing endogenous Pot1 from telomeres. Reducing telomere-bound Pot1 in this manner resulted in dramatic lengthening of the telomere tract. Upon further reduction of Pot1 at telomeres, the opposite phenotype was observed: loss of telomeric DNA and chromosome end fusions. Our results demonstrate that cells must carefully regulate the amount of telomere-bound Pot1 to differentiate between allowing access to telomerase and catastrophic loss of telomeres.
authors.affiliation: Stowers Institute for Medical Research, 1000 E. 50th Street, Kansas City, Missouri 64110, USA.
authors.forename: Jeremy T
authors.initials: JT
authors.lastname: Bunch
authors.forename: Nancy S
authors.initials: NS
authors.lastname: Bae
authors.forename: Jessica
authors.initials: J
authors.lastname: Leonardi
authors.forename: Peter
authors.initials: P
authors.lastname: Baumann
mesh_terms: D000595:Amino Acid Sequence; D043171:Chromosomal Instability; D015825:Chromosomes, Fungal; D005656:Fungal Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D008969:Molecular Sequence Data; D009154:Mutation; D017434:Protein Structure, Tertiary; D017386:Sequence Homology, Amino Acid; D019098:Telomerase / Q000378:metabolism; D016615:Telomere / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D034501:Telomere-Binding Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*
chemical_list: D005656:Fungal Proteins; D034501:Telomere-Binding Proteins; D019098:Telomerase