Concept explainers
A species of bacteria can synthesize the amino acid histidine, so they do not require histidine in their growth medium. A key enzyme, which we will call histidinesynthetase, is necessary for histidine biosynthesis. When these bacteria are given histidine in their growth medium, they stop synthesizing histidineintracellularly. Based on this observation alone, propose three different regulatory mechanisms to explain why histidine biosynthesis ceases when histidine is in the growth medium. To explore this phenomenon further, you measure the amount of intracellular histidinesynthetase protein when cells are grown in the presence and absence of histidine. In both conditions, the amount of this protein is identical. Which mechanism of regulation is consistent with this observation?
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Genetics: Analysis and Principles
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