DNA gyrase negatively supercoils closed circular double-stranded DNA in an ATP-dependent manner to maintain chromosomes in an underwound state (PubMed:186775, PubMed:3031051, PubMed:1323022, PubMed:8248233, PubMed:7811004, PubMed:8621650, PubMed:9657678, PubMed:12051842, PubMed:12051843, PubMed:18642932, PubMed:19060136, PubMed:19965760, PubMed:22457353, PubMed:23294697, PubMed:20356737, PubMed:20675723, PubMed:23352267, PubMed:24386374, PubMed:25202966, PubMed:25849408). This makes better substrates for topoisomerase 4 (ParC and ParE) which is the main enzyme that unlinks newly replicated chromosomes in E.coli (PubMed:9334322). Gyrase catalyzes the interconversion of other topological isomers of double-stranded DNA rings, including catenanes (PubMed:22457352). Relaxes negatively supercoiled DNA in an ATP-independent manner (PubMed:337300). E.coli gyrase has higher supercoiling activity than other characterized bacterial gyrases; at comparable concentrations E.coli gyrase introduces more supercoils faster than M.tuberculosis gyrase, while M.tuberculosis gyrase has higher decatenation than supercoiling activity compared to E.coli (PubMed:22457352). E.coli makes 15% more negative supercoils in pBR322 plasmid DNA than S.typhimurium; the S.typhimurium GyrB subunit is toxic in E.coli, while the E.coli copy can be expressed in S.typhimurium even though the 2 subunits have 777/804 residues identical (PubMed:17400739). The enzymatic differences between E.coli gyrase and topoisomerase IV are largely due to the GyrA C-terminal domain (approximately residues 524-841) and specifically the GyrA-box (PubMed:8962066, PubMed:16332690). ATP-dependent breakage, passage and rejoining of double-stranded DNA. Binds two Mg(2+) per subunit. The magnesium ions form salt bridges with both the protein and the DNA. Can also accept other divalent metal cations, such as Mn(2+) or Ca(2+) (PubMed:12051843, PubMed:18642932). Binds one K(+) per subunit which interacts with the alpha-phosphate of ATP analog and stimulates ATPase activity of the N-terminal fragment; Na(+) or water bind less well (PubMed:25849408). Binds one Na(+) per subunit, with 4 ligands provided by water; may be able to bind K(+), the functional significance of this ion is unclear (PubMed:25849408). Gyrase is the target of many classes of inhibitors, including coumarins, cyclothialidines, pyrrolopyrimidines, pyrazolthiazoles and (fluoro)quinolones. Coumarins bind to GyrB and are competitive inhibitors of its ATPase activity (PubMed:7811004). Cyclothialidines also bind GyrB and are ATPase competitive inhibitors; they seem to act differently from coumarins (PubMed:7811004, PubMed:8635474). Pyrrolopyrimidines inhibit both GyrB and its paralog in topoisomerase 4 (parE) (PubMed:23294697, PubMed:23352267, PubMed:24386374). Pyrazolthiazoles also inhibit the ATPase activity of GyrB (PubMed:20356737). Quinolones bind GyrA when the enzyme is complexed with DNA and trap the enzyme in a covalent reaction intermediate with DNA (PubMed:3031051, PubMed:12051842, PubMed:337300). Acriflavine inhibits DNA supercoiling and DNA-stimulated ATPase activity (PubMed:9148951). DNA supercoiling activity is protected from fluoroquinolone inhibition by QnrB4; QnrB4 has no effect on supercoiling activity alone (PubMed:19060136). Heterotetramer, composed of two GyrA and two GyrB chains (PubMed:9148951, PubMed:12051842). In the heterotetramer, GyrA contains the active site tyrosine that forms a transient covalent intermediate with the DNA, while GyrB binds cofactors and catalyzes ATP hydrolysis (PubMed:12051843, PubMed:18642932, PubMed:20675723, PubMed:19965760). Consists of 3 domains; the ATPase domain (residues 1-220), the transducer domain (221-392) and the toprim domain (393-804) (PubMed:1646964, PubMed:10734094). ATP-binding is cooperative, and both subunits must be wild-type at residue 103 for supercoiling to occur (PubMed:8621650). Non-hydrolyzable ATP analogs (and ATP-binding) induce dimerization and enhance ATPase activity (PubMed:10734094, PubMed:9657678). ATP hydrolysis induces domain shifts that are probably part of the mechanism of DNA cleavage and rejoining (PubMed:25202966). When the enzyme transiently cleaves DNA a phosphotyrosine bond is formed between GyrA and DNA in an ATP-independent manner (PubMed:3031051). In the presence of quinolones this intermediate can be trapped and is used as an indicator of drug toxicity (PubMed:12051842). Belongs to the type II topoisomerase family.