Characterization of a unique type IA topoisomerase in Bacillus cereus

Abstract

Bacillus cereus topoisomerase IIIβ (bcTopo IIIβ) has been cloned, overexpressed and biochemically characterized. This enzyme exhibits 64% and 33% sequence identity to Bacillus subtilis topoisomerase III (bsTopo III) and Escherichia coli topoisomerase III (ecTopo III) respectively. The enzymatic properties of bcTopo IIIβ differ substantially from other bacterial type IA topoisomerases, including E. coli type IA topoisomerases and B. cereus topoisomerase I (bcTopo I) and IIIα (bcTopo IIIα). bcTopo IIIβ only partially relaxes negatively supercoiled DNA and appears incapable of generating fully relaxed topoisomers. In contrast to ecTopo III and bcTopo IIIα, bcTopo IIIβ is not a decatenase. bcTopo IIIβ is unable to compensate the loss of ecTopo III in vivo. Therefore, bcTopo IIIβ is a unique prokaryotic type IA topoisomerase that is different from previously characterized topoisomerases. © 2006 Blackwell Publishing Ltd.