Extended Data Fig. 8: Structural conservation of Tetrahymena PolαPrim.
From: Structure of Tetrahymena telomerase-bound CST with polymerase α-primase
a, Superposition of Tetrahymena (Tt), human and yeast POLA1core structures45,46,47,73,74 shown in an overall view. b, Structural comparison of PolαPrim platform of Tt and human45,46. The structures were superposed based on POLA2–POLA1CTD (left) or PRIM1 (right). Arrows indicate dynamics of the unaligned regions. PRIM2C in human structures are shown as transparent ribbons. PRIM2C is not observed in the Tt structure. c, Structures of PolαPrim in an autoinhibited conformation (left, modelled on the basis of PDB 5EXR45) and an active conformation (right, modelled on the basis of a low-resolution cryo-EM map in Extended Data Fig. 7a). The DNA-DNA duplexes on POLA1core were modelled on the basis of PDB 5IUD47. In the autoinhibited conformation (left), the active site on POLA1core is sterically blocked by POLA1CTD and POLA2 for DNA entry. In the active conformation (right), dynamics of subunits are indicated with arrows. d-e, Superposition of Tt, human and yeast POLA1core structures for the regions that are on the interface with TtCST. Conserved domains/motifs are labeled as indicated. The β11-β12 hairpin in Tt POLA1core is longer than those in human and yeast (d). The α19 is structured only in Tt POLA1 when binding TtCST (e). f, Close-up views of the interface between Tt POLA1core α19 (ribbon) and TtCST (surface/electrostatic surface). In the lower panel, locations of positively and negatively charged residues on α19 are indicated using blue and red balls, respectively. g, Sequence-conservation analysis of the β11-β12 hairpin and α19 of POLA1. Charged residues on α19 are indicated with black arrows. h, Close-up view of the interface between POLA1core and TtCST with sstDNA. Cryo-EM densities are shown as transparent surface. The template entry port formed by POLA1core NTD and Exo and Ctc1 OB-C is indicated by a cycle. i, Path of sstDNA in the cryo-EM structure of Tt telomerase–PolαPrim. The sstDNA binds in the C-shape cleft of Ctc1 OB-C with its 5' side, while its 3' side passes through the template entry port to the active site of POLA1core (left). A G-quadruplex (GQ) formed by four Tt telomere repeats (modelled on the basis of PDB 7JKU48) is observed on a positively charged DNA binding surface of POLA1core between the palm and thumb (right). j, Superimposition of the GQ structure and cryo-EM density. Weak density of sstDNA can be observed connecting the sstDNA on Ctc1 OB-C to the GQ.
