[Theoretical model of the B-Z transition in DNA with an arbitrary sequence].

A statistical-mechanical model is suggested that makes it possible to describe the B-Z transition in DNA with an arbitrary sequence of nucleotides. The key point consists in allowance for the fact that each base pair can assume one of the two states with different energies. One of these states corresponds to the standard Z-form with purines in the syn conformation and pyrimidines in the anti conformation. However, in natural DNA sequences such standard base-pair conformations should be interrupted by energetically unfavorable conformations (syn for pyrimidines and anti for purines). Open regions and cruciform structures are also allowed for in the model. The probabilities of formation of the Z-form stretches, open regions and cruciform structures have been calculated for different values of parameters for pBR322 and pAO3 DNA.