Figure 7.

 Substrates containing telomeric repeats at any position are bound by p95 and elongated by telomerase. (A) A 36-nucleotide oligonucleotide with two repeats of telomeric sequence at the 3′ end and two repeats of a 12-nucleotide nontelomeric cassette at the 5′ end was radiolabeled and assayed at 40 nm with 100 nm p95. The p95 shift of this probe (lane 2) was competed (lanes 3–14) with sequences altered in the position of the telomeric repeats. Competitor concentrations were 5-, 50-, and 500-fold that of the probe concentration. Open bars indicate nontelomeric sequence; solid bars indicate telomeric sequence. (B) The same 36-nucleotide primers as in A were used as substrates for elongation in activity assays with purified telomerase. Each primer was used at a concentration of 200 nm or 2 μm (equal to the lowest two competitor concentrations above). (Lanes 1,2) Elongation of the standard 18-nucleotide d(G₄T₂)₃ for comparison.