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Historical Perspective, Page 1 of 2
< Previous page Next page > /docserver/preview/fulltext/10.1128/9781555818319/9781555810894_Chap01-1.gif /docserver/preview/fulltext/10.1128/9781555818319/9781555810894_Chap01-2.gifAbstract:
Mutations in either crp or cya of Escherichia coli resulted in the same phenotype: the inability to grow on many carbon compounds other than glucose. The contributions of the products of the two genes could be distinguished by the observation that the growth defect of the cya mutants but not that of the crp mutants could be corrected by the addition of cyclic AMP (cAMP) to the growth medium, indicating that these mutants lack the enzyme necessary for the synthesis of cAMP. The inducible phenotype of the wild-type strain depends on the normal function of two genes, hutC, the structural gene for the repressor, and hutU, the structural gene for urocanase, the enzyme responsible for the degradation of urocanate, the product of histidase. The important characteristic of two-component systems is therefore the covalent modification of the effector by the modulator. Apparently, the domains of the proteins evolved independently and were then combined. It is likely that effectors dependent on phosphorylation by phosphodonors of low molecular weight existed before the evolution of specific modulators.