REGULATION OF AMMONIUM ION ASSIMILATION ENZYMES IN NEUROSPORA-CRASSA NIT-2 AND MS-5 MUTANT STRAINS

In Neurospora crassa the nit-2 and nmr-1 (ms-5) loci represent the maj or control genes encoding regulatory proteins that allow the coordinat ed expression of various systems involved with the utilization of a se condary nitrogen source. In this paper we examine the effect of the ni t-2 and ms-5 (nmr-1 locus) mutations on the regulation of the ammonium assimilation enzymes, glutamine synthetase and glutamate dehydrogenas e, which are regulated by the products of these genes; however, glutam ate synthase is not so regulated. Glutamine synthetase and glutamate d ehydrogenase levels are also regulated by the amino nitrogen content. We present evidence that the ms-5 and gln(r) strains which behave very similarly in their resistance to glutamine repression, are different and map in different loci.