Endonuclease II of Escherichia coli: DNA reacted with 7-bromomethyl-12-methylbenz[alpha]anthracene as a substrate.

An endonuclease II preparation from Escherichia coli makes single strand breaks in DNA which has been treated with the carcinogen 7-bromomethyl-12-methylbenz[alpha]anthracene. In addition, the enzyme preparation excises N6-(12-methylbenz[alpha]anthracenyl-7-methyl)adenine and N2-(12-methylbenz[alpha]anthracenyl-7-methyl)guanine residues from the DNA. These are relased as the modified purine bases, not as purine nucleoside derivatives. The rate of release of the adenine derivative is three to four times that of the guanine derivative.