Prokaryotic type I DNA topoisomerase [56712] (1) duplication: the protein chain passing through the domains 2-4 makes two structural repeats The active site is formed by the toprim and "winged helix" domains (domains 1 and 4); these two domains are also found in the type II topoisomerase (DNA gyrase A) and in the alpha subunit of topoisomerase IV uperfamily