Fig. 5.
The DNA overstretching transition at 110 pN is a melting transition. (A) Images of two different 3′5′-5′3′ attached DNA molecules labeled with the ssDNA marker eGFP-RPA, one held at a tension of 95 pN (before the onset of the OS transition) and the other at 135 pN (beyond the transition). At force below the transition, no eGFP-RPA binding is observed. Beyond the transition, eGFP-RPA covers the DNA homogeneously and completely. (B) Images of two different 3′5′-5′3′ attached DNA molecules at a tension of 110 pN labeled sequentially with eGFP-RPA (Top), and dsDNA-intercalator POPO (Bottom). eGFP-RPA binds throughout the DNA molecules and no unique nucleation point can be observed.