Statistical mechanics of RNA folding: a lattice approach.

We propose a lattice model for the secondary structure of RNA based on a self-interacting two-tolerant trail. Self-avoidance and pseudoknots are taken into account. We investigate a simple version of the model in which the native state of RNA consists of just one hairpin. Using exact arguments and Monte Carlo simulations we determine the phase diagram for this case. We show that the denaturation transition is first order and can either occur directly or through an intermediate molten phase.