Fig. 1. CST–Polα–primase uses telomeric repeats as origins of priming and replication.
a, Time courses of C-strand synthesis on telomeric DNA templates, with products labelled with [α-32P]dCTP. Size markers are telomerase reaction products with end-labelled primer (T-end, 5′-phosphate) and body-labelled products (T-body, 5′-hydroxyl) as described in Methods. LC, labelled oligonucleotide loading control. b, Quantification of C-strand synthesis products in the experiment directly above. c, Model explaining the observed 6-nt ladders of C-strand reaction products. CST–Polα–primase binds the template (grey) at different sets of telomeric repeats, such that runoff synthesis gives products in 6-nt increments. The binding site shown at the top (initiation site 1) gives the purple C-strand product, while initiation at sites 2 and 3 gives the green and red products, respectively. In each case, the RNA primer is indicated by a lighter shade and telomeric repeats are indicated by vertical bars. The location of CST relative to Polα–primase and the template DNA is taken from the recent cryo-EM structure32. For gel source data, see Supplementary Fig. 1.