A Rapid Assay for Dna Photolyase Using a Membrane‐binding Technique*

A rapid assay for DNA photolyase was developed that makes use of the membrane binding technique of A. D. Riggs, H. Suzuki and S. Bourgeois, J. Mol. Biol. 48 , 67–83 (1970). The complex formed between UV‐irradiated bacteriophage T7 DNA‐ 3 H and the enzyme is trapped on a nitrocellulose filter after a five‐minute equilibration and is counted. Using this technique, one can calculate the molar concentration of enzyme in an enzyme preparation and the saturation constant (K) for the complex formation. The latter value is 2.6 cyclobutadipyrimidines per genome (T7) for yeast DNA photolyase; thus approximately 5.2 dipyrimidines/genome are necessary for the full retention of the DNA on the membrane. The speed and reproducibility of the new method makes it a convenient one for assaying column effluents and as many as one hundred samples can be handled routinely in an afternoon.