1. e.10.1 Prokaryotic type I DNA topoisomerase 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 ! Prokaryotic type I DNA topoisomerase 4 domains: (1) Toprim alpha/beta; (2&4) "winged helix"-like; (3) barrel: n=6, S=8 1gku d1gkub3 B:58-71,72-77,504-513,534-542,544-553 1gl9 d1gl9c3 C:58-71,72-77,505-513,534-543,544-553 1gl9 d1gl9b3 B:58-71,72-77,505-513,534-543,544-553