ENDONUCLEASE IN CULTURE SUPERNATANTS AND CELL-FREE EXTRACTS OF E. COLI K12 STRAINS
ARMY BIOLOGICAL LABS FREDERICK MD
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The deoxyribonuclease activities of culture supernatant fluids and crude sonic extracts of various substrains of Escherichia coli are reported. The assay methods consisted of measuring the description of transforming Bacillus licheniformis DNA, and the appearance of acid-soluble materials absorbing ultraviolet light at 260 millimicrons. Culture supernatants of F and Hfr strains in most cases inactivated transforming DNA to a greater extent than supernatants of F- strains. Sonic extracts also destroyed transforming DNA and no difference in activity was noted among F-, F, and Hfr strains. Acid- soluble materials absorbing ultraviolet light at 260 millimicrons increased slowly when all extracts were incubated with calf thymus DNA. Calf thymus DNA protected transforming DNA from destruction in the presence of cell-free extracts. The rapid destruction of transforming DNA by culture supernatants and cell-free extracts and the slow appearance of acid-soluble materials suggest that extracellular and intracellular endonuclease activity is responsible for the observed effects.