Regulation of amino acid synthetic enzymes in Neurospora crassa in the presence of high concentrations of amino acids.

Ornithine carbamoyl transferase and leucine aminotransferase of Neurospora crassa represent two of many amino acid synthetic enzymes which are regulated through cross-pathway (or general) amino acid control. In the wild-type strain both enzymes display derepressed activities if the growth medium is supplemented with high (mM range) concentrations of L-amino acids derived from branched pathways, i.e. the aspartate, pyruvate, glycerophosphate and aromatic families of amino acids. A cpc-1 mutant strain, impaired in cross-pathway regulation i.e. lacking the ability to derepress, shows delayed growth under such conditions. In the presence of glycine, homoserine and isoleucine various cpc-1 isolates do not grow at all. Derepression of the wild-type enzymes and the retarded growth of the mutant strain can be reversed if certain amino acids are present in the medium in addition to the inhibitory amino acids.