Purification of the yeast PHR1 photolyase from an Escherichia coli overproducing strain and characterization of the intrinsic chromophores of the enzyme.

We have placed the PHR1 gene of Saccharomyces cerevisiae under the transcriptional and translational control of the tac expression cartridge. Under inducing conditions Escherichia coli cells harboring plasmids carrying this construct accumulate approximately 8% of total cellular protein as the Phr1 photolyase. Using a strain devoid of E. coli photolyase activity, we have obtained milligram quantities of the yeast enzyme at greater than 95% purity and have characterized the enzyme. Phr1 photolyase is a monomer in solution with an Mr of 60,000, has a turnover number of 0.7 dimers min-1 molecule-1 in vitro, exhibits absorbance maxima at lambda = 277 and 377 nm, and has a fluorescence excitation maximum at 390 nm and an emission maximum at 475 nm. The near UV absorbance peak is shown to reflect the contributions of two intrinsic chromophores which are noncovalently bound to the enzyme. Spectroscopic, fluorescence, and thin layer chromatographic studies indicate that one of these chromophores is 1,5-reduced FAD rather than 4a,5-reduced FAD as previously proposed (Iwatsuki, N., Joe, C. O., and Werbin, H. (1980) Biochemistry 19, 1172-1176), while the other chromophore has properties similar to the second chromophore of E. coli photolyase. The fact that yeast and E. coli photolyases are similar both with respect to amino acid sequence and chromophore composition provides strong evidence that the enzymes share a common action mechanism which may also be utilized by photolyases from other organisms throughout the phylogenetic tree.