Telomere length homeostasis is achieved via a switch between telomerase- extendible and -nonextendible states

Cell. 2004 Apr 30;117(3):323-35. doi: 10.1016/s0092-8674(04)00334-4.


Telomerase counteracts telomere erosion that stems from incomplete chromosome end replication and nucleolytic processing. A precise understanding of telomere length homeostasis has been hampered by the lack of assays that delineate the nonuniform telomere extension events of single chromosome molecules. Here, we measure telomere elongation at nucleotide resolution in Saccharomyces cerevisiae. The number of nucleotides added to a telomere in a single cell cycle varies between a few to more than 100 nucleotides and is independent of telomere length. Telomerase does not act on every telomere in each cell cycle, however. Instead, it exhibits an increasing preference for telomeres as their lengths decline. Deletion of the telomeric proteins Rif1 or Rif2 gives rise to longer telomeres by increasing the frequency of elongation events. Thus, by taking a molecular snapshot of a single round of telomere replication, we demonstrate that telomere length homeostasis is achieved via a switch between telomerase-extendible and -nonextendible states.

Publication types

  • Comparative Study
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Base Sequence
  • Cell Cycle
  • Chromosomes, Fungal / metabolism
  • Crosses, Genetic
  • DNA / analysis
  • Gene Expression Regulation, Enzymologic
  • Gene Expression Regulation, Fungal
  • Genetic Variation
  • Homeostasis*
  • Kinetics
  • Models, Biological
  • Polymerase Chain Reaction
  • Recombination, Genetic
  • Saccharomyces cerevisiae / enzymology*
  • Saccharomyces cerevisiae / genetics
  • Saccharomyces cerevisiae Proteins / metabolism
  • Telomerase / deficiency
  • Telomerase / genetics
  • Telomerase / metabolism*
  • Telomere / genetics
  • Telomere / metabolism*


  • Saccharomyces cerevisiae Proteins
  • DNA
  • Telomerase