COMPUTATIONAL APPROACH TO THE STUDY OF SUPERCOIL-INDUCED STRUCTURAL POLYMORPHISM IN DNA

The superhelical strain in a closed circular B DNA molecule may be rel ieved at the cost of local conformational transitions to non-B forms w herever possible. Some of these transitions, such as the supercoil-ind uced B-Z transition in a short purine-pyrimidine stretch, are known to be highly cooperative and can be described in terms of a two-state ap proximation for the relevant chain partition function. How the presenc e of DNA-binding ligands may affect such transitions within the superc oiled molecule has been analysed. The result of a preliminary investig ation into the effect of sharp bends in the supercoiled DNA structure is also reported.