NEW MUTATIONAL VARIANTS OF NEUROSPORA NADP-SPECIFIC GLUTAMATE DEHYDROGENASE

The am locus of Neurospora codes for NADP-dependent glutamate dehydrogenase (GDH). Four new am mutants that produced mutationally altered GDH have been characterized. Mutant am  119 is a CRM-negative, complementing mutant that maps between am  2 and am  1. The other three mutants are CRM formers that produce varieties of GDH that can be activated by glutamate or succinate. The GDH of am  130 and am  l31 is similar in terms of activation properties to that of am  3. The GDH of am  l22, requires very high concentrations of dicarboxylate for activity. The mutation in am  l30 maps between am  l4 and am  2 and resulted in a replacement at residue 75 of the GDH (pro→ser). The mutation in am  l22 maps near am  ll and apparently resulted in the replacement of the tryptophan residue at position 389 with an unknown amino acid. The mutation in am  l31 maps between am  2 and am  1.