It has been shown previously that the DNA deoxyribophosphodiesterase (dRpase) activity of Escherichia coli excises 2-deoxyribose 5-phosphate moieties at apurinic/apyrimidinic (AP) sites in DNA following cleavage of the DNA at the AP site by an AP endonuclease such as endonuclease IV of E. coli. A second class of enzymes that cleave DNA at AP sites by a β-elimination mechanism, AP lyases, leave a different sugar-phosphate product remaining at the AP site, which has been identified as the compound trans-4-hydroxy-2-pentenal 5-phosphate. It is shown that dRpase removes this unsaturated sugar-phosphate group following cleavage of a poly(dA-dT) substrate containing AP sites by the action of the AP lyase endonuclease III of E. coli. The Km for the removal of trans-4-hydroxy-2-pentenal 5-phosphate is 0.06 μM; the Km for the removal of 2-deoxyribose 5-phosphate is 0.17 μM. It was verified that the sugar-phosphate product removed by dRpase from the endonuclease III-cleaved substrate was trans-4-hydroxy-2-pentenal 5-phosphate by conversion of the product to the compound cyclopentane-1,2-dione. The dRpase activity is unique in its ability to remove sugar-phosphate products after cleavage by both AP endonucleases and AP lyases.

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