Cryo-electron microscopy structure of the budding yeast telomerase holoenzyme

Telomerase is a reverse transcriptase that synthesizes telomeric repeats at chromosome ends, safeguarding genome integrity. We present the cryo-electron microscopy structure of the budding yeast telomerase, which exhibits substantial divergence from its ciliate and vertebrate counterparts. The structure reveals a stable core formed by telomerase RNA TLC1; the three ever shorter telomere (Est) proteins, Est1, Est2 and Est3; and the Pop1/Pop6/Pop7 complex (Pop1/6/7). TLC1, Est3, and Pop1/6/7 serve critical roles in complex assembly. We identified a zinc finger (ZnF) motif in the telomerase reverse transcriptase (TERT) subunit Est2 that is crucial for telomerase function. Structure prediction suggests the presence of ZnFs in TERT from diverse species. These findings offer insights into the functional organization of yeast telomerase and underscore the evolutionary diversity of telomerase holoenzymes.