Regulation of tryptophan metabolism in Coprinus cinereus: Isolation and characterisation of mutants resistant to 5-fluoroindole

171 mutations conferring resistance to the indole analogue 5-fluoroindole (5 FI) were isolated in the filamentous basidiomycete fungus Coprinus cinereus. 5 FI is thought to be toxic because it is converted intracellularly to 5-fluorotryptophan (5 FT) which feedback inhibits the first enzyme of the tryptophan biosynthetic pathway, anthranilate synthase. Mutations were assigned to five loci, iar-1-iar-5 on the basis of functional analyses and mapping experiments. iar-5 mutations mapped in the anthranilate synthase structural gene and gave rise to an enzyme feedback resistant to tryptophan and its analogue. Mutants at other loci had regulatory changes. iar-1 and iar-3 mutants had elevated levels of two pathway enzymes measured (anthranilate synthase and tryptophan synthase) and were cross resistant to analogues of other aromatic amino acids suggesting that the entire aromatic pathway was derepressed. iar-3 mutants were unable to degrade metabolically derived typtophan to anthranilic acid unlike iar-1 mutants which excreted high levels of anthranilic acid. iar-2 mutants appeared to have a constitutive degradative pathway. iar-4 mutants had a blocked degradative pathway and unusual levels of tryptophan pathway enzymes.