Genetic Regulatory Mechanisms in the Fungi
There are at least two interdependent signals controlling the production, by three unlinked structural genes, of the three leucine biosynthetic enzymes of Neurospora (1). Leucine represses the first enzyme, α-isopropylmalate synthetase (the synthetase), the product of the leu-4 cistron. The synthetase catalyzes the production of α-isopropylmalate (α-IPM), which is the second signal—an obligate inducer for the synthesis of α-IPM isomerase (the isomerase) and β-IPM dehydrogenase (the dehydrogenase), specified, respectively, by the leu-2 and leu-1 cistrons. Endogenous α-IPM concentrations respond inversely to endogenous leucine concentration, not only because leucine represses synthetase formation but more importantly because leucine feedback inhibits the catalytic activity of the synthetase (1, 2).
KeywordsLeucine Concentration Genetic Regulatory Mechanism Amino Acid Binding Site Leucine Biosynthetic Pathway Type Wild Type
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