Figure 1. A novel telomere-specific RPA displacing activity in human cell extracts.

a, POT-TPP1 (60 nM; purified from insect cells), RPA (60 nM), and mixtures of POT1-TPP1 and RPA (60, 120, 180 nM of POT1-TPP1 mixed with 60 nM of RPA) were incubated with 20 nM of the ssDNA probe and analyzed by gel-shift. b, POT1-TPP1 (2.4 nM), RPA (2.4 nM), and mixtures of POT1-TPP1 and RPA (2.4, 4.8, 7.2 nM of POT1-TPP1 mixed with 2.4 nM of RPA) were incubated with 0.8 nM of biotinylated ssTEL [(TTAGGG)₈]. The proteins bound to ssTEL were retrieved by streptavidin beads and analyzed by Western blot. c, Biotinylated ssTEL or ssMUT [(TTTGCG)₈] was incubated with WCEs or recombinant RPA (rRPA). d, ssTEL or ssMUT precoated with RPA was incubated with increasing concentrations of HeLa WCEs (0.08, 0.19, 0.36, 0.8, 1.3 μg/μl). The RPA2 remaining on ssTEL was analyzed as in b. e, ssTEL precoated with POT1 was incubated with increasing concentrations of HeLa WCEs (0.07, 0.18, 0.33, 0.66, 1.3 μg/μl).