Yeast strains were constructed in which a single telomere could be eli
minated from the end of a dispensable chromosome. In wild-type cells,
elimination of a telomere caused a RAD9-mediated cell cycle arrest, in
dicating that telomeres help cells to distinguish intact chromosomes f
rom damaged DNA. However, many cells recovered from the arrest without
repairing the damaged chromosome, replicating and segregating it for
as many as ten cell divisions prior to its eventual loss. Telomere eli
mination caused a dramatic increase in loss of the chromosome in all s
trains examined, demonstrating that yeast telomeres are also essential
for maintaining chromosome stability. Thus, in spite of checkpoint an
d DNA damage repair systems, many chromosomes that lose a telomere are
themselves destined for loss.