An endonuclease from Escherichia coli that introduces single polynucleotide chain scissions in ultraviolet-irradiated DNA.

An endonuclease that makes single polynucleotide chain scissions in ultraviolet-irradiated DNA has been purified from Escherichia coli. The activity has the following properties: (a) unirradiated DNA is attacked very little if at all; (b) single strand DNA is not attacked, whether irradiated or not; (c) there is no requirement for divalent cations and the activity is not affected by the addition of EDTA; (d) the pH optimum is approximately 7; (e) the activity is inhibited by 1 M NaCl, single strand DNA, transfer RNA and double strand DNA; (f) the sedimentation coefficient, S20,w, is approximately 2.6; (g) it is a basic protein. The enzyme is tentatively named E. coli endonuclease III. The physiological function of the endonuclease has not yet been established.