Telomere maintenance without telomerase.

Recombination-dependent maintenance of telomeres, first discovered in budding yeast, has revealed an alternative pathway for telomere maintenance that does not require the enzyme telomerase. Experiments conducted in two budding yeasts, S. cerevisiae and K. lactis, have shown recombination can replenish terminal G-rich telomeric tracts that would otherwise shorten in the absence of telomerase, as well as disperse and amplify sub-telomeric repeat elements. Investigation of the genetic requirements for this process have revealed that at least two different recombination pathways, defined by RAD50 and RAD51, can promote telomere maintenance. Although critically short telomeres are very recombinogenic, recombination among telomeres that have only partially shortened in the absence of telomerase can also contribute to telomerase-independent survival. These observations provide new insights into the mechanism(s) by which recombination can restore telomere function in yeast, and suggest future experiments for the investigation of potentially similar pathways in human cells.