Deoxyribonucleic Acid Photoreactivating Enzyme from Escherichia coli

DNA photoreactivating enzyme has been purified from Escherichia coli B and from induced cells of an E. coli strain containing a lysogenic bacteriophage carrying the gene for photoreactivation. The final preparations appear homogeneous by the criteria of presence of one band after electrophoresis on polyacrylamide gels under nondenaturing conditions and of constant specific activity in enzyme fractions eluted from hydroxylapatite. The enzyme has an apparent monomer molecular weight between 40,000 and 46,000 and tends to aggregate in solution. The pH optimum under the present assay conditions is 7.2. The action spectrum for photoreactivation by the purified enzyme has a maximum in the same region and the same spectral shape as the action spectrum obtained for E. coli cells in vivo.