AP endonuclease and uracil DNA glycosylase activities in Deinococcus radiodurans

An endonuclease specific for apurinic/apyrimidinic (AP) sites was identified and purified from extracts of Deinococcus radiodurans. The enzyme is 34.5 kD, has no activity towards normal, alkylated, uracil-containing, or UV-irradiated DNA, and is active in the presence of EDTA. The addition of up to 10 mM Mg2+ or Mn2+ did not affect activity, but higher concentrations were inhibitory. There is no associated exonuclease activity, either in the presence or absence of divalent cation. Optimal reaction conditions were 150 mM NaCl and pH 7.5. A uracil DNA glycosylase was also detected, active in the presence of EDTA, selectively removing uracil from DNA without generating other byproducts. The optimal reaction conditions were 50 mM NaCl and pH 7.5. Implications for base excision repair in D. radiodurans are discussed.