Heat-activated endonuclease in Bacillus subtilis.

A heat-stable, heat-activated endonuclease was found in sonic extracts of the transformable strain Bacillus subtilis 168 when the organism was grown to logarithmic phase in minimal medium. The enzyme was not present in the poorly transformable strain 23. The endonuclease was stable to 100 C for 30 min and, in a crude extract, was activated by heating at 80, 90, or 100 C. The activation caused a 5- to 10-fold increase in total units of enzyme activity. Sucrose gradient centrifugation indicated that the enzyme in a crude preparation has a major form (molecular weight, 66,000) which remains unchanged after heat activation. Under the assay conditions employed, the endonuclease did not release acid-soluble material from the substrate, high molecular weight tritiated deoxyribonucleic acid. The product, in double-stranded form, had a molecular weight of approximately 10(5), but it appeared to have undergone single-strand breaks.