RNA condensation and the wetting transition.

We present a continuum theory for the condensation of large, soluble, single-stranded RNA molecules on attractive substrates. In the mean-field approximation, the theory reduces to the Cahn-de Gennes description of wetting fluids and offers a natural explanation for the development of a sharply defined density profile following a prewetting surface phase transition. This mapping onto the wetting problem can break down because of a capillary instability where the adsorbed film decomposes into a collection of segregated, nonoverlapping molecules.