The regulatory role of DNA supercoiling in nucleoprotein complex assembly and genetic activity

We argue that dynamic changes in DNA supercoilingin vivo determine both how DNA is packaged and how it is accessed for transcription and for other manipulations such as recombination. In both bacteria and eukaryotes, the principal generators of DNA superhelicity are DNA translocases, supplemented in bacteria by DNA gyrase. By generating gradients of superhelicity upstream and downstream of their site of activity, translocasesenable the differential binding of proteins which preferentially interact with respectively more untwisted or more writhedDNA. Such preferences enable, in principle, the sequential binding of different classes of protein and so constitute an essential driver of chromatin organization.