Читать книгу Snyder and Champness Molecular Genetics of Bacteria - Tina M. Henkin - Страница 112

Bacteria have several type I topoisomerases. The major bacterial type I topoisomerase removes negative supercoils from DNA. In E. coli and Salmonella enterica serovar Typhimurium, the topA gene encodes this type I topoisomerase. As expected, DNA isolated from E. coli with a topA mutation is more negatively supercoiled than normal.

Figure 1.27 Action of the two types of topoisomerases. The type I topoisomerases break one strand of DNA and pass the other strand through the break, removing one supercoil at a time. The type II topoisomerases break both strands and pass another part of the same DNA through the breaks, introducing or removing two supercoils at a time.