Isolation, characterization, and activation of the magnesium dependent endodeoxyribonuclease from Bacillus subtilis

A major endodeoxyribonulcease was isolated from a mutant of the transformable Bacillus subtilis 168. The magnesium-dependent endonuclease was purified approximately 750-fold to electrophoretic homogeneity. The enzyme had a molecular weight of about 31 000, as determined by gel filtration and polyacrylamide gel electrophoresis. The protein appears to be composed of two subunits. The nuclease was dependent on magnesium or maganese ions for hydrolytic activity. The purified nuclease degraded DNA from several species of Bacillus, as well as Escherichia coli DNA, alkylated, depurinated, and thymine-dimer containing B. subtilis DNA, and hydroxymethyluracil-containing phage DNA. The enzyme also hydrolyzed single-stranded DNA, although native DNA was the preferred substrate. However, the nuclease was unable to degrade ribosomal RNA. The cleavage products of the DNA hydrolysis have 5'-phosphate and 3'-hydroxyl ends. The enzyme could be activated in crude extracts by heat treatment or treatment with guanidine hydrochloride. The nuclease activity was inhibited by phosphate and by high concentrations of NaCl. A possible function for this endonuclease in bacterial transformation is discussed.