Effects of mechanical strain on thermal denaturation of DNA

A class of simple statistical mechanical models for DNA melting, first proposed by Poland and Scheraga, have been demonstrated to exhibit first or second order thermodynamic singularity, notwithstanding the intrinsic one-dimensional nature of the problem. In the present paper we show that the inclusion of twist elastic energy in the Poland-Scheraga models either leads to suppression of the thermodynamic singularity or to a weak, third order singularity.