A yeast telomerase complex containing the Est1 recruitment protein is assembled early in the cell cycle

In budding yeast, association of the Est1 regulatory protein with telomerase is thought to be limited to the late S phase, when telomere elongation occurs. By monitoring the stoichiometry of telomerase subunits, we show instead that a telomerase complex containing Est1 is assembled much earlier in the cell cycle. We also report a biochemical interaction between Est1 and the telomere binding protein Cdc13 that recapitulates the previously observed genetic relationship between EST1 and CDC13. This supports a model in which regulated binding of Cdc13 to chromosome termini dictates subsequent interaction of a recruitment-competent telomerase complex with telomeres.