3 EVER SHORTER TELOMERE (EST) GENES ARE DISPENSABLE FOR IN-VITRO YEAST TELOMERASE ACTIVITY

Telomerase is a specialized reverse transcriptase consisting of both R NA and protein components, Previous characterization of yeast telomera se function in vivo identified four EST (for ever shorter telomeres) g enes that, when mutated, result in the phenotypes expected for a defec t in telomerase. Consistent with this genetic prediction, the EST2 gen e has recently been shown to encode the catalytic component of telomer ase. Using an in vitro assay, we show here that telomerase activity is present in extracts prepared from yeast strains carrying est1-Delta, est3-Delta, and cdc13-2(est) mutations, Therefore, while these three g enes are necessary for telomerase function in vivo, they do not encode components essential for core catalytic activity, When Est2p, the one EST gene product found to be essential for catalytic activity, was im munoprecipitated from extracts, the telomerase RNA subunit was also sp ecifically precipitated, supporting the conclusion that these two comp onents are in a stable complex.