Bacterial and archeal type I topoisomerases.

Bacterial and archeal type I topoisomerases, including topoisomerase I, topoisomerase III and reverse gyrase, have different potential roles in the control of DNA topology including regulation of supercoiling and maintenance of genetic stability. Analysis of their coding sequences in different organisms shows that they belong to the type IA family of DNA topoisomerases, but there is variability in organization of various enzymatic domains necessary for topoisomerase activity. The torus-like structure of the conserved transesterification domain with the active site tyrosine for DNA cleavage/rejoining suggests steps of enzyme conformational change driven by DNA substrate and Mg(II) cofactor binding, that are required for catalysis of change in DNA linking number.