The one gene one enzyme stated by Beedle and Tatum that each gene controls a single specific enzyme. By x-ray, they produced nutritional mutants in bread mould Neurospora crassa that were unable to synthesize pyridoxin or thiamine or biotin. Such mutants therefore were suspected to have a metabolic defect because of inability to synthesize some substances normally synthesized by the wild type Neurospora. Genetic crosses between the Neurospora wild type and the many mutants isolated revealed that growth of most of the mutants were impaired due to the mutation of single gene in the Neurospora genome. Furthermore, detailed biochemical study of the aberrant metabolism of the mutants showed that most of them carry a block at a single step in the reaction sequence leading up to the synthesis of amino acid, vitamin, purine or pyrimidine required for growth. On the basis of these facts, Beedle and Tatum now asserts that each gene has only one primary function of directing the formation of one and only enzyme. In this way Beedle and Tatum were able to demonstrate in each case that ability to synthesize a biochemical product was governed by a single gene. Another proof for this hypothesis came from arginine biosynthesis pathway in E.coli. The pathway consists of eight chemical reactions each catalysed by a specific enzyme. The presence of each enzyme, in turn, is controlled by a single distinct gene. Specific enzymes are known; the absence of each enzyme is due to a single and distinct mutant gene. Mutants of gene 1 cannot utilize the first substrate glutamine; mutants of gene 2 can utilise glutamine but not the product of it, N-acetylglutamate. Similarly other mutants cannot utilize the product of a step due to absence of an enzyme fallowing mutation.
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| Arginine biosynthesis in E.coli |
