Mutants of Bacillus subtilis deficient in urocanase or in imidazolonepropionate hydrolase were isolated. These mutants are unable to use l-histidine as source of carbon or nitrogen for growth. The enzymes are thus essential for the metabolism of histidine. The structural genes specifying these enzymes are closely linked to those specifying the other two enzymes essential for histidine degradation, histidase, and formiminoglutamate hydrolase. The response of these enzymes to induction and catabolite repression is specified by a region of the chromosome closely linked to one end of the cluster of structural genes. The gene cluster presumably constitutes an operon.
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Kimhi et al. (1970) studied this question.
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