Partial purification and characterization of a uracil-DNA glycosylase from wheat germ

A uracil-DNA glycosylase has been purified over 1,000-fold from wheat germ, the first such repair activity isolated from a higher plant. The enzyme has a molecular weight of approximately 27,000 and is resistant to metal ion chelators, but inhibited by high concentrations of either mono or divalent cations. This glycosylase is unable to release uracil from the mononucleotides dUMP and dUTP or from wheat germ RNA. Twelve pyrimidine analogues which closely mimic uracil structurally and the nucleoside uridine were examined for their ability to inhibit glycosylase activity. However, only 5-azauracil and 6-aminouracil inhibited enzymatic release of uracil to the same degree as uracil itself. An inhibitor induced by bacteriophage T5 which inhibits Escherichia coli uracil-DNA glycosylase has been shown not to affect the glycosylase isolated from wheat germ, indicating that these two enzymes differ. The ability of the wheat germ uracil-DNA glycosylase to completely remove available uracil from synthetic DNA substrates in which thymine had been replaced by uracil in varying percentages was also examined and found not to depend on percentage of uracil in the substrates.