title: Enzymic unwinding of DNA. 2. Chain separation by an ATP-dependent DNA unwinding enzyme.
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 detectably 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.
mesh_terms: D000251:Adenosine Triphosphatases / Q000494:pharmacology*; D004247:DNA; D004277:DNA, Single-Stranded; D004926:Escherichia coli / Q000201:enzymology; D066298:In Vitro Techniques; D007700:Kinetics; D008956:Models, Chemical; D009691:Nucleic Acid Denaturation / Q000187:drug effects*; D009693:Nucleic Acid Hybridization
chemical_list: D004277:DNA, Single-Stranded; D004247:DNA; D000251:Adenosine Triphosphatases