Mutational synergism between p-fluorophenylalanine and UV in Coprinus lagopus

Previous studies have shown that the amino acid analogue p-fluorophenylalanine (PFP) is mutagenic to Coprinus lagopus due to its incorporation into proteins [32]. Spontaneous mutations, PFP and UV mutagenesis and PFP/UV synergism have been studied in a UV resistant strain and in two complementing UV sensitive mutant strains. By comparison to the UV resistant strain, one UV sensitive strain shows normal spontaneous mutations, 1.4% PFP-induced mutations and 50-fold UV mutagenesis. The second UV sensitive strain has 19-fold spontaneous mutation frequency, 8% PFP induced mutations and slightly elevated UV mutagenesis. In all 3 strains the PFP/UV synergism is comparable (4--5 times the arithmetic expected). The results indicate that PFP mutagenesis is due to the incorporation of PFP into enzymes normally functioning in the organism but which also participate in UV repair mechanisms. A model is proposed for UV repair which is based on a PFP sensitive excision repair system of at least two enzymes, and alternative "error proof" pathway which is not suscetible to PFP and an "error prone" pathway which is responsible for UV mutagenesis and is susceptible to PFP as shown by the PFP/UV synergism. Because PFP is given before UV treatment, this implies a UV inducible cofactor and a PFP sensitive enzyme which only functions after UV activation.