gyrB (Escherichia coli K12):   DNA gyrase, subunit B; DNA gyrase negatively supercoils closed circular double- stranded DNA in an ATP-dependent manner to maintain chromosomes in an underwound state. This makes better substrates for topoisomerase 4 (ParC and ParE) which is the main enzyme that unlinks newly replicated chromosomes in E.coli. Gyrase catalyzes the interconversion of other topological isomers of double-stranded DNA rings, including catenanes. Relaxes negatively supercoiled DNA in an ATP-independent manner. E.coli gyrase has higher supercoiling activity than other characterized bacterial gyrases; at compa [...]