DNA PHOTOLYASE FROM THE FUNGUS NEUROSPORA CRASSA. PURIFICATION, CHARACTERIZATION AND COMPARISON WITH OTHER PHOTOLYASES

Abstract A phr‐gene from the filamentous fungus Neurosporu crassa was overexpressed in Escherichia coli cells, yielding a biologically active photolyase. After purification till apparent homogeneity, the 66 kDa protein was found to contain equimolar amounts of 5,1O‐methenyltetrahydrofolic acid (MTHF) and FAD, classifying it as an MTHF‐type photolyase. Compared to other MTHF photolyases the absorption maximum of Neurosporu photolyase is shifted from ca 380 nm to 391 nm (t = 34 800), while an additional shoulder is present at 465 nm. In dark‐adapted enzyme the FAD chromophore is predominantly present in the oxidized form, in contrast with E. coli and Saccharomyces cerevisiue photolyase, which contain mainly semiquinone or fully reduced FAD, respectively. Preillumination or dithionite treatment converted oxidized FAD in Neurospora photolyase into the fully reduced form, with a concomitant shift of the absorption maximum from 391 to 396 nm and disappearance of the 465 nm shoulder. The action spectrum of photoreactivation coincides with the absorption spectrum of preilluminated (reduced) photolyase, extending the spectral region of MTHF‐type photolyases from 380 till 396 nm. A quantum yield of 0.57 was obtained for the overall repair reaction. Comparison of spectral properties of FAD in Neurospora photolyase and the model compound lumiflavin points to an apolar microenvironment of photolyase‐bound FAD. Neurosporu photolyase has distinct advantages over E. coli photolyase as it is more stable and contains a full complement of chromophores.