Читать книгу Structure and Function of the Bacterial Genome - Charles J. Dorman - Страница 37

DNA in bacterial cells is maintained in an underwound state and this affects the shape that the DNA duplex adopts as it seeks to adopt a minimal energy conformation. The underwinding arises due to a deficit in helical turns, i.e. the number of times the two DNA strands twist around the duplex axis. The twist deficiency imparts torsional stress to the duplex, which is relieved by allowing the duplex to adopt a writhed confirmation in which the helical axis coils around itself. This coiling of the already coiled DNA duplex creates supercoiling and has the effect of making the DNA molecule more compact. In the context of the nucleoid, such compaction assists with solving the problem of packaging the genetic material within the cell. The most supercoiled parts of the chromosome form branches, facilitating further compaction.