Differential Response of a Double Mutant–adenineless, Inositolless-in Neurospora Crassa to Combined Treatment by Ultra-violet Radiation and Chemicals

Abstract

The effect of combined treatment with ultra-violet light and formaldehyde or H2O2 on the reverse-mutation rate of 2 alleles of Neurospora crassa has been investigated. The reverse-mutation rate of 1 mutant allele, adenineless, is greatly enhanced by combining ultra-violet radiation with pre- or post-treatment with both chemicals, whereas the reverse-mutation rate of the other allele, inositolless, may be slightly decreased. Reconstruction experiments show that this differential response of the 2 alleles cannot be explained by differential killing. These results are discussed in relation to the theories of the "indirect" or "direct" effect of radiation, and the experiments are interpreted as suggesting that in 1 case (inositol reversions) mutations are caused by a direct effect, whereas indirect radiochemical processes are mainly responsible for the induction of back mutations in the adenine allele. A number of experiments have been outlined by which this hypothesis can be further tested.