Modulation of telomere terminal structure by telomerase components in Candida albicans

The telomerase ribonucleoprotein in Candida albicans is presumed to contain at least three Est proteins: CaEst1p, CaEst2p/TERT and CaEst3p. We constructed mutants missing each of the protein subunit of telomerase and analyzed overall telomere dynamics and single-stranded telomere overhangs over the course of many generations. The est1-DeltaDelta mutant manifested abrupt telomere loss and recovery, consistent with heightened recombination. Both the est2-DeltaDelta and est3-DeltaDelta mutant exhibited progressive telomere loss, followed by the gradual emergence of survivors with long telomeres. In no case was telomere loss accompanied by severe growth defects, suggesting that cells with short telomeres can continue to proliferate. Furthermore, the amount of G-strand terminal overhangs was greatly increased in the est2-DeltaDelta mutant, but not others. Our results suggest that in addition to their well-characterized function in telomere elongation, both CaEst1p and CaEst2p mediate some aspects of telomere protection in Candida, with the former suppressing excessive recombination, and the latter preventing excessive C-strand degradation.