Purification of Escherichia coli endonuclease specific for apurinic sites in DNA

The endonuclease specific for apurinic sites in DNA has been isolated from Escherichia coli B41 as a pure monomeric protein of 32,000 daltons. The enzyme hydrolyzes a phosphodiester bond near the apurinic sites in double-stranded DNA; it does not hydrolyze untreated DNA and its action on alkylated DNA is restricted to the apurinic sites always present. This enzyme is not endonuclease II which is most probably a mixture of two enzymes, one a glycosidase (Kirtikar, D. M., and Goldthwait, D. A. (1974) Proc. Natl. Acad. Sci. U. S. A. 71, 2022-2026), the other an endonuclease for apurinic sites which is the enzyme isolated in this work.