Purification and properties of the endonuclease specific for apurinic sites of Bacillus stearothermophilus.

An endonuclease specific for apurinic sites when double-stranded DNA is used as substrate has been isolated from the thermophilic bacterium, Bacillus stearothermophilus; it is a monomeric protein of about 28,000 daltons, without action on normal DNA strands or on alkylated sites. The enzyme is quite thermoresistant in the presence of other proteins, has an optimal temperature of 60 degrees, needs monovalent cations for optimal activity, is insensitive to EDTA, and is inhibited by divalent cations; it has no associated exonuclease activity. These latter properties are closer to those of Escherichia coli thermoresistant endonuclease IV, which is also insensitive to EDTA and has no exonuclease activity, and very different from those of the main endonuclease for apurinic sites of the same bacterium. The B. stearothermophilus enzyme is more resistant to urea and detergents than the main E. coli endonuclease for apurinic sites and has a higher content of hydrophobic amino acids.