Title: A Neurospora crassa mutant altered in the regulation of L-amino acid oxidase
Abstract: The isolation and characterization of a Neurospora crassa mutant altered in l-amino oxidase regulation is reported. The previously isolated gln-1bR8 strain, which only synthesizes the glutamine synthetase α monomer and lacks the β monomer, was used as parental strain. A mutant derivative of strain was selected for its ability to grow on minimal medium in the presence of DL -methionine- SR -sulfoximine (MSO), an inhibitor of glutamine synthetase activity. This gln-1bR8;MSO R mutant overcame the inhibitory effect of MSO by increasing the activity of L -amino acid oxidase, an enzyme capable of degrading this compound. In contrast with the wild-type strain, the L -amino acid oxidase of the MSO R mutant was resistant to glutamine repression; in fact, it was induced by this amino acid but repressed by ammonium. This mutant is different from other nitrogen regulatory N. crassa mutants reported and is only altered in the regulation of L -amino acid oxidase. The MSO R mutation is epistatic to nit -2 since the nit2;MSO R double mutant regulated the L -amino acid oxidase in the same way as the MSO R single mutant.