; Wang Ping
; Meng Ying-Hong] Chinese Acad Sci, Inst High Energy Phys, Beijing 100049, Peoples R China
; [Wang Ping
; Meng Ying-Hong] Chinese Acad Sci, Grad Sch, Beijing 100049, Peoples R China
We propose an Ashkin-Teller-like model for elastic response of DNA molecule to external force and torque. The base-stacking interaction is described in a simple and uniform way. We obtain the phase diagram of dsDNA, and in particular, the transition from B form to the S state induced by stretching and twisting. The elastic response of the ssDNA is presented also in a unified formalism. The close relation, of dsDNA molecule structure with elastic response is shown clearly. The calculated folding angle of the dsDNA molecule is 59.2 degrees.