Uracil-DNA glycosylase. Purification and properties of uracil-DNA glycosylase from Micrococcus luteus.

A uracil-DNA-glycosylase from Micrococcus luteus has been purified more than 3,000-fold. The enzyme preparation appears homogeneous, according to the results of sodium dodecyl sulfate-polyacrylamide gel electrophoresis. It is devoid of nonspecific endonucleases, specific endonucleases for apurinic and apyrimidinic sites, 3-methyladenine or 7-methylguanine-DNA-glycosylases. It behaves as a monomer protein of 19,400 daltons. It has an isoelectric point of 7.0 +/- 0.1. It has an optimal activity between pH 5.0 and 7.0. It has no cofactor requirement and is not inhibited by EDTA. Uracil-DNA-glycosylase is highly specific for DNA containing dUMP residues, releasing uracil as product of the reaction. It is 2-fold more active on single-stranded DNA than on double-stranded DNA. If it releases uracil dimers from ultraviolet-irradiated PBS1 DNA, it is at the threshold of the detection. The apparent Km is 7 X 10(-8) M, and uracil acts as a noncompetitive inhibitor with a Ki of 3.2 X 10(-4) M. Cis-syn cyclogbutadiuracil also is a potent inhibitor, while some analogs, produced by x-irradiation of uracil and thymine, are weak inhibitors. Spermine, between 10 and 400 microM, increases the enzymatic activity by 50% and is not inhibitory at other concentrations. Spermidine activates the enzyme at concentrations of 40 to 120 microM, but becomes inhibitory at 200 and 400 microM. A new finding is that drugs which intercalate in DNA, such as ethidium bromide and ellipticine, cause a 2- to 2.5-fold activation of this enzyme activity. The concentrations giving maximal activation depend on the drug. The enzyme does not behave as a processive enzyme during uracil excision.