Biopolymers and cell. 1997; 13 (1): 39 - 45

A structural-dynamic model on spontaneous semiopen states in DNA

D. M. Hovorun

In this work there is suggested a structural-dynamic model on semiopen states in a two-strand DNA based on the semiempirical quantum-mechanical MNDO/H investigation of topologic properties of potential energy hyperfurface of free Watson-Crick Ade:Thy and GiuuCyt pairs. In the frame of this model semiopen methastable states of Ade:Thy rich DNA sites are related to the spontaneous methastable state of Ade:Thy Watson-Crick pair, which is stabilized by two intrapair N3H...N1 and C2H...O2 hydrogen bonds, the Ade amino group being released from an H-bond. Therewith virtual semiopen states of the GuaCyt pair which are formed as a result of the turn of Gua and Cyt amino groups to cis- and trans-position with respect to the adjacent C2N3 bonds are believed to be a predecessors of methastable semiopen DNA states, arising in the Gua-'Cyt rich sites at much higher temperature. The author is opinion that the virtual semiopen states favour to the formation of induced (for examle by interactions with ligands of various nature) semiopen states. A number of experimental facts explained in the frame of the proposed model confirm its adequacy.