Aromatic amino acid biosynthesis and para-fluorophenylalanine resistance inAspergillus nidulans

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Abstract
1. Five additional phenylalanine (PHE)-requiring mutants have been isolated but they do not add to the number of loci already known which have been designatedphenA(phen2and its alleles) andphenB(phen6).2. Two pathways for tyrosine (TYR) synthesis inA. nidulanshave been proposed: the well-known one by the transamination ofp-hydroxyphenylpyruvic acid and an alternative one, as in animals, by the hydroxylation of PHE.3. Ten allelic partial TYR-requiring mutants (tyrA), presumably blocked in the transamination pathway, have been isolated after N-methyl-N′-nitro-N-nitrosoguanidine (NTG) treatment ofbil;phenA3 conidia.4. Four partial TYR requirers (at another locus—tyrB) have been isolated after NTG treatment oftyr A7, bi1conidia. They are presumably blocked in an alternative pathway for TYR synthesis, i.e. in the PHE-hydroxylation pathway.5.tyrAmutants have been found to bep-fluorophenylalanine (FPA)-resistant and allelic to mutants at thefpAlocus.tyrBmutants have been found to be very leaky and FPA-sensitive.tyrA;tyrBdouble mutants have been found to be exacting TYR requirers.6. Mutants at locifpA(tyrA) andfpE(anthranilic acid-requiring) have been interpreted to bep-fluorophenylalanine-resistant due to an oversynthesis of PHE.