The est1 mutant was previously identified because it is defective in telomere maintenance and displays a senescent phenotype. To see if Est1 might be a component of yeast telomerase, we examined immunoprecipitated Est1. The yeast telomerase RNA Tlc1 specifically coprecipitated with Est1. Furthermore, the Est1 immunoprecipitates con- tained a telomerase-like activity. As expected for yeast telo- merase, the activity elongated telomeric primers, it required dGTP and dTTP but not dATP or dCTP, and it was sensitive to RNase A.
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