SNAP output for PDB entry 7uy7 [SNAP web server]

PDB-id

7uy7; SNAP-derived features in text and JSON formats; DNAproDB

Class

replication

Method

cryo-EM (4.2 Å)

Summary

Tetrahymena cst with polymerase alpha-primase

Reference

He Y, Song H, Chan H, Liu B, Wang Y, Susac L, Zhou ZH, Feigon J (2022): "Structure of Tetrahymena telomerase-bound CST with polymerase alpha-primase." Nature, 608, 813-818. doi: 10.1038/s41586-022-04931-7.

Abstract

Telomeres are the physical ends of linear chromosomes. They are composed of short repeating sequences (such as TTGGGG in the G-strand for Tetrahymena thermophila) of double-stranded DNA with a single-strand 3' overhang of the G-strand and, in humans, the six shelterin proteins: TPP1, POT1, TRF1, TRF2, RAP1 and TIN2_1,2. TPP1 and POT1 associate with the 3' overhang, with POT1 binding the G-strand₃ and TPP1 (in complex with TIN2₄) recruiting telomerase via interaction with telomerase reverse transcriptase₅ (TERT). The telomere DNA ends are replicated and maintained by telomerase₆, for the G-strand, and subsequently DNA polymerase α-primase_7,8 (PolαPrim), for the C-strand₉. PolαPrim activity is stimulated by the heterotrimeric complex CTC1-STN1-TEN1_10-12 (CST), but the structural basis of the recruitment of PolαPrim and CST to telomere ends remains unknown. Here we report cryo-electron microscopy (cryo-EM) structures of Tetrahymena CST in the context of the telomerase holoenzyme, in both the absence and the presence of PolαPrim, and of PolαPrim alone. Tetrahymena Ctc1 binds telomerase subunit p50, a TPP1 orthologue, on a flexible Ctc1 binding motif revealed by cryo-EM and NMR spectroscopy. The PolαPrim polymerase subunit POLA1 binds Ctc1 and Stn1, and its interface with Ctc1 forms an entry port for G-strand DNA to the POLA1 active site. We thus provide a snapshot of four key components that are required for telomeric DNA synthesis in a single active complex-telomerase-core ribonucleoprotein, p50, CST and PolαPrim-that provides insights into the recruitment of CST and PolαPrim and the handoff between G-strand and C-strand synthesis.