Temperature dependence of two distinct DNA overstretching transitions

Recent experiments show that two distinct transitions are involved in the DNA overstretching that occurs at around 65 pN: a strand-unpeeling transition leading to strand separation from free DNA ends or nicks, and a B to S transition leading to an overstretched double-stranded DNA called ``S-DNA.'' Here we show that the two transitions have distinct temperature dependence: in the strand-unpeeling transition, the transition force decreases when the temperature increases; while in the B to S transition, the temperature dependence of the transition force is opposite. Our results are in agreement with the notion that the two transitions involve distinct types of double-helix reorganization.