Principles of Genetic Regulation in Lower and Higher Plants
Living organisms are generally able to adapt themselves to relatively wide and sudden variations of the environmental conditions. As a result of a change in their surroundings, they may produce one or several additional enzymes specifically related to the new external conditions, This property of adaptation may be easily demonstrated with unicellular organisms the metabolism of which is strongly dependent on the growth medium. If a yeast cell is transferred from its normal medium containing mineral nitrogen to a medium containing arginine as the sole nitrogen source, it will rapidly synthesize two enzymes (arginase and ornithine transaminase) which are needed for degrading arginine into NH 4 + and glutamate . The production of great amounts of these two enzymes will allow the cell to make all its nitrogenous compounds from arginine. Hence, the induction of arginine breakdown enzymes is a prerequisite for survival of the yeast in these particular conditions, That the repression of enzyme synthesis is a prerequisite for survival is also obvious. Certain species of Pseudomonas are able to grow on more than 100 different organic substrates .
KeywordsStructural Gene Nitrate Reductase Nitrate Reductase Activity Regulation Mutant Sole Nitrogen Source
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