The Nature of Photoactivation in Neurospora crassa

Lethal effects produced by far ultraviolet light (254 nm) in Neurospora crassa conidia can be reversed by light of longer wavelengths (310 to 450 nm) administered after UV. Action spectra indicate that the most effective wavelengths for photoreactivation of N. crassa are in the 400-nm region, in contrast with Escherichia coli and Streptomyces griseus, where the peak efficiencies are around 365 nm and 440 nm, respectively. The rate of reactivation is dependent on the temperature during illumination. Extracts of N. crassa conidia with light of the proper wavelengths will repair UV-irradiated Hemophilus influenzae transforming DNA in vitro. The action spectrum, temperature dependence, and ability of extracts to reverse UV damage in vitro suggest that photoreactivation of lethal damage in N. crassa is of the direct type, and involves light-dependent repair enzymes.