Reversibility of replicative senescence in Saccharomyces cerevisiae: effect of homologous recombination and cell cycle checkpoints.

Primary human somatic cells grown in culture divide a finite number of times, exhibiting progressive changes in metabolism and morphology before cessation of cycling. This telomere-initiated cellular senescence occurs because cells have halted production of telomerase, a DNA polymerase required for stabilization of chromosome ends. Telomerase-deficient Saccharomyces cerevisiae cells undergo a similar process, with most cells arresting growth after approximately 60 generations.