[Cleavage of bacteriophage PM2 DNA by S1 nuclease]

The kinetics of cleavage of superhelical PM2 DNA by the single strand-specific S1 nuclease is studied at various salt concentrations (0.01--1 MNaCl) by electrophoresis in neutral and alkaline agarose gels. Cleavage of different DNA forms (superhelical DNA I, relaxed circular DNA II and linear DNA III) is described by the kinetic equations of the first order, and respective rate constants k1, k2, and k3 are determined at all salt concentrations used. It is shown that a high salt concentration (not lower than 0.2 MNaCl) is necessary for high specificity of S1 nuclease action on DNA regions with impaired base pairing. Examination of the S1 nuclease preparation action on superhelical PM2 DNA may be used as a convenient and reliable assay of its specificity.