Extended Data Fig. 4: Electron microscopy density of hTR and DNA substrate.

a, Secondary structure schematic of hTR based on the structure. This figure was modified from the telomerase database⁷⁰. b, c, Full density of hTR in the catalytic core (b) and the H/ACA lobe (c). d, Close-up view of the density of interactions between the DNA substrate and hTR template (Fig. 2b). e, Close-up view of density of the DNA substrate and neighbouring residues of TERT (Extended Data Fig. 6d). f, Close-up view of density of the RNA template region and neighbouring residues of TERT (Extended Data Fig. 6e). g, Density of the P6.1 hairpin of the CR4/5 domain. Labelled residues are highlighted in Fig. 3a. h, Close-up review of the density of the P6.1 stem loop interacting with residues of the CTE domain of TERT (g, Fig. 3a). i, Close-up view of the density of residue L1019 of TERT, which interacts with the two flipped-out nucleotides, U177 of the PK and U307 of the P6.1 stem loop as highlighted in Fig. 3b. j, Representative density of the PK containing the base triples, which are highlighted in black. Nucleotide U113 is modelled but not visible in this view. k, Density of the H and ACA boxes (Extended Data Fig. 3p). l, Density of the P8 stem loop (Extended Data Fig. 3o).