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Abstract

The DNA‐stimulated ATPase characterized in the accompanying paper is shown to be a DNA unwinding enzyme. Substrates employed were DNA · RNA hybrid duplexes and DNA · DNA partial duplexes prepared by polymerization on fd phage single‐stranded DNA template. The enzyme was found to denature these duplexes in an ATP‐dependent reaction, without delectably degrading. EDTA, an inhibitor of the Mg2+ ‐requiring ATPase, was found to prevent denaturation suggesting that dephosphorylation of the ATP and not only its presence is required. These results together with those from enzyme‐DNA binding studies lead to ideas regarding the mode of enzymic action. It is proposed that the enzyme binds, in an initial step, to a single‐stranded part of the DNA substrate molecule and that from here, energetically supported by ATP dephosphorylation, it invades double‐stranded parts separating base‐paired strands by processive, zipper‐like action. It is further proposed that chain separation results from the combined action of several enzyme molecules and that a tendency of the enzyme to aggregate with itself reflects a tendency of the molecules to cooperate. Various functions are conceivable for the enzyme.