Distinct requirements for Pot1 in limiting telomere length and maintaining chromosome stability

Mol Cell Biol. 2005 Jul;25(13):5567-78. doi: 10.1128/MCB.25.13.5567-5578.2005.


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.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amino Acid Sequence
  • Chromosomal Instability*
  • Chromosomes, Fungal
  • Fungal Proteins / chemistry
  • Fungal Proteins / genetics
  • Fungal Proteins / metabolism*
  • Molecular Sequence Data
  • Mutation
  • Protein Structure, Tertiary
  • Sequence Homology, Amino Acid
  • Telomerase / metabolism
  • Telomere / chemistry
  • Telomere / genetics
  • Telomere / metabolism*
  • Telomere-Binding Proteins / chemistry
  • Telomere-Binding Proteins / genetics
  • Telomere-Binding Proteins / metabolism*


  • Fungal Proteins
  • Telomere-Binding Proteins
  • Telomerase