| Type: | Domain | Name: | DNA topoisomerase, type IA, central region, subdomain 3 |
| Description: | DNA topoisomerases regulate the number of topological links between two DNA strands (i.e. change the number of superhelical turns) by catalysing transient single- or double-strand breaks, crossing the strands through one another, then resealing the breaks []. These enzymes have several functions: to remove DNA supercoils during transcription and DNA replication; for strand breakage during recombination; for chromosome condensation; and to disentangle intertwined DNA during mitosis [, ]. DNA topoisomerases are divided into two classes: type I enzymes (; topoisomerases I, III and V) break single-strand DNA, and type II enzymes (; topoisomerases II, IV and VI) break double-strand DNA [].Type I topoisomerases are ATP-independent enzymes (except for reverse gyrase), and can be subdivided according to their structure and reaction mechanisms: type IA (bacterial and archaeal topoisomerase I, topoisomerase III and reverse gyrase) and type IB (eukaryotic topoisomerase I and topoisomerase V). These enzymes are primarily responsible for relaxing positively and/or negatively supercoiled DNA, except for reverse gyrase, which can introduce positive supercoils into DNA. Type IA topoisomerases are comprised of four domains that together form a toroidal structure with a central hole large enough to accommodate single- and double-stranded DNA: an N-terminal alpha/beta Toprim domain, domain 2 and the C-terminal domain 4 are winged-helix domains, and domain 3 is a beta-barrel. Domains 1 (Toprim) and 3 form the active site of the enzyme, while the winged helix domains 2 and 4 form a single-strand DNA-binding groove [, ]. This entry represents the alpha-bundle subdomain 3 of the central region of topoisomerase type IA enzymes, where the central region covers both domains 2 and 3. | Short Name: | Topo_IA_cen_sub3 |
