Selective Inhibition of the DNase Activity of the recBC Enzyme by the DNA Binding Protein from Escherichia COG*

In the pesence of the Escherichia coli DNA binding protein, single-stranded DNA is resistant to both the endoand exonucleolytic activities of the recBC DNase. Linear duplex DNA, on the other hand, is unwound at a normal rate, but converted to large, single-stranded fragments which are resistant to further hydrolysis. Therefore, in the presence of the binding protein and linear duplex DNA, the recBC enzyme acts not as a DNase, but primarily as an ATP-dependent unwinding enzyme, able to generate large, single-stranded material. Duplex circular DNA containing short, single-stranded gaps is also resistant to the hydrolysis in the presence of the binding protein.