title: The product of the leu-3 cistron as a regulatory element for the production of the leucine biosynthetic enzymes of Neurospora.
abstract: A class of intracistronic (or closely linked) partial reversions of leu-3 mutations has been found to be conditionally constitutive with respect to the synthesis of isopropylmalate isomerase (specified by the leu-2 cistron) and beta-isopropylmalate dehydrogenase (specified by the leu-1 cistron), two of the enzymes of leucine biosynthesis in Neurospora. The intermediate level of enzyme production by these leu-3(cc) mutants is independent of the obligatory inducer effector, alpha-isopropylmalate, but dependent upon the presence of the branched-chain amino acids, isoleucine, valine and leucine. The properties of leu-3+, leu-3 and leu-3(cc) in heterokaryons indicate that the transnuclear regulatory activity of the leu-3 product varies specifically as a function of available effector molecules. The information presented suggests that the leu-3 cistron is responsible not only for the production of a "positive" regulatory substance necessary for the expression of the leu-1 and leu-2 cistrons, but that it probably serves also a coordinating role in the expression of many of the genes involved in branched-chain amino acid metabolism.
mesh_terms: D000429:Alcohol Oxidoreductases / Q000378:metabolism; D000483:Alleles; D003470:Culture Media; D003998:Dicarboxylic Acids; D004790:Enzyme Induction; D005809:Genes, Regulator; D005838:Genotype; D007294:Inositol / Q000378:metabolism; D007532:Isoleucine / Q000494:pharmacology; D007535:Isomerases / Q000378:metabolism; D007651:Keto Acids; D007930:Leucine / Q000096:biosynthesis* / Q000494:pharmacology; D008293:Malates; D009154:Mutation; D009491:Neurospora / Q000201:enzymology* / Q000254:growth & development; D007652:Oxo-Acid-Lyases / Q000037:antagonists & inhibitors / Q000378:metabolism; D010205:Pantothenic Acid / Q000378:metabolism; D013696:Temperature; D014633:Valine / Q000494:pharmacology
chemical_list: D003470:Culture Media; D003998:Dicarboxylic Acids; D007651:Keto Acids; D008293:Malates; D007532:Isoleucine; D010205:Pantothenic Acid; D007294:Inositol; D000429:Alcohol Oxidoreductases; D007652:Oxo-Acid-Lyases; D007535:Isomerases; D007930:Leucine; D014633:Valine