Modulation of the relaxing activity of Escherichia coli topoisomerase I by single-stranded DNA binding proteins.

Removal of negative superhelical turns in ColE1 plasmid DNA by Escherichia coli topoisomerase I was markedly enhanced by the presence of single-stranded DNA binding protein from E. coli. A lack of species specificity makes unlikely the possibility of physical association between topoisomerase I and single-stranded DNA binding proteins. Stabilization of single-stranded regions in supercoiled DNA by single-stranded DNA binding protein would appear to be the basis of the enhancement of topoisomerase activity.