A NEUROSPORA-CRASSA MUTANT ALTERED IN THE REGULATION OF L-AMINO-ACID OXIDASE

The isolation and characterization of a Neurospora crassa mutant alter ed in L-amino oxidase regulation is reported. The previously isolated gln-1bR8 strain, which only synthesizes the glutamine synthetase alpha monomer and lacks the beta monomer, was used as parental strain. A mu tant derivative of strain was selected for its ability to grow on mini mal medium in the presence of DL-methionine-SR-sulfoximine (MSG), an i nhibitor of glutamine synthetase activity. This gln-1bR8;MSOR mutant o vercame the inhibitory effect of MSO by increasing the activity of L-a mino acid oxidase, an enzyme capable of degrading this compound. In co ntrast with the wild-type strain, the L-amino acid oxidase of the MSOR mutant was resistant to glutamine repression; in fact, it was induced by this amino acid but repressed by ammonium. This mutant is differen t from other nitrogen regulatory N. crassa mutants reported and is onl y altered in the regulation of L-amino acid oxidase. The MSOR mutation is epistatic to nit-2 since the nit2;MSOR double mutant regulated the L-amino acid oxidase in the same way as the MSOR single mutant.