| Type: | Family | Name: | DNA topoisomerase I, bacterial-type |
| 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 topoisomerase I from bacteria, which is more closely related to archaeal than to eukaryotic topoisomerase I []. Topoisomerase I is the major enzyme for relaxing negatively supercoiled DNA, and its presence is balanced by reverse gyrase, which can introduce negative supercoils. Prokaryotic topoisomerase I folds in an unusual way to give 4 distinct domains, enclosing a hole large enough to accommodate a double-stranded DNA segment. A tyrosine at the active site, which lies at the interface of 2 domains, is involved in transient breakage of a DNA strand, and the formation of a covalent protein-DNA intermediate through a 5'-phosphotyrosine linkage. The structure reveals a plausible mechanism by which this and related enzymes could catalyse the passage of one DNA strand through a transient break in another strand []. Topoisomerase I require Mg2+ as a cofactor for catalysis to take place. | Short Name: | TopoI_bac-type |
| DB identifier | Type | Name |
|---|---|---|
| IPR013824 | Domain | DNA topoisomerase, type IA, central region, subdomain 1 |
| IPR013497 | Domain | DNA topoisomerase, type IA, central |
| IPR013498 | Domain | DNA topoisomerase, type IA, zn finger |
| IPR003602 | Domain | DNA topoisomerase, type IA, DNA-binding domain |
| IPR003601 | Domain | DNA topoisomerase, type IA, domain 2 |
| GO Term | Gene Name |
|---|---|
| GO:0003677 | IPR005733 |
| GO:0003917 | IPR005733 |
| GO:0006265 | IPR005733 |
