RecQ helicase and topoisomerase III comprise a novel DNA strand passage function: A conserved mechanism for control of DNA recombination

E. coli RecQ protein is a multifunctional helicase with homologs that inclu de the S. cerevisiae Sgs1 helicase and the H. sapiens Wrn and Blm helicases . Here we show that RecQ helicase unwinds a covalently closed double-strand ed DNA (dsDNA) substrate and that this activity specifically stimulates E. coli topoisomerase III (Topo III) to fully catenate dsDNA molecules. We pro pose that these proteins functionally interact and that their shared activi ty is responsible for control of DNA recombination. RecQ helicase has a com parable effect on the Topo III homolog of S. cerevisiae, consistent with ot her RecQ and Topo III homologs acting together in a similar capacity. These findings highlight a novel, conserved activity that offers insight into th e function of the other RecQ-like helicases.