| Type: | Domain | Name: | DNA topoisomerase, type IA, domain 2 |
| 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. This entry describes domain 2 found in type IA topoisomerases, which may be an extension of the Toprim domain. The structures of bacterial topoisomerases I and III have been shown to consist of four domains that together form a toroidal structure with a central hole large enough to accommodate single- and double-stranded DNA. The N-terminal Toprim domain together with domain 3 forms the active site of the enzyme, while domains 2 and 4 form a single-strand DNA-binding groove [, ]. The Toprim domain () forms a compact Rossmann fold that coordinates the Mg+2 ion []. | Short Name: | Topo_IA_2 |
| DB identifier | Type | Name |
|---|---|---|
| IPR005733 | Family | DNA topoisomerase I, bacterial-type |
| IPR000380 | Family | DNA topoisomerase, type IA |
| IPR013824 | Domain | DNA topoisomerase, type IA, central region, subdomain 1 |
| IPR013497 | Domain | DNA topoisomerase, type IA, central |
| IPR005738 | Family | DNA topoisomerase III |
| IPR005739 | Family | DNA topoisomerase I, archeal-type |
| IPR005736 | Family | Reverse gyrase |
| GO Term | Gene Name |
|---|---|
| GO:0003677 | IPR003601 |
| GO:0003916 | IPR003601 |
| GO:0006265 | IPR003601 |
