Induction and Repression of the Histidine-degrading Enzymes of Bacillus subtilis

Abstract In Bacillus subtilis a series of four enzymes is responsible for the degradation of l-histidine to ammonia, formamide, and l-glutamic acid. The third enzyme of the series was not investigated; the other three enzymes, histidase, urocanase, and formiminoglutamate hydrolase, are induced by l-histidine and repressed by catabolites. Mutants can be found in which the three enzymes are constitutive but still subject to catabolite repression. In other mutants the three enzymes are insensitive to catabolite repression but still inducible. In addition, a mutant simultaneously constitutive and resistant to catabolite repression and a mutant incapable of producing any one of the three enzymes were found. Other mutants are deficient only in histidase or only in formiminoglutamate hydrolase. The arrangement of the genes affecting the formation of these enzymes was studied by transformation. All genes are closely linked in the order: catabolite repression-inducibility-histidase-formiminoglutamate hydrolase. The mutation causing both constitutivity and insensitivity to catabolite repression may be a deletion. The site whose mutation causes inability to produce any one of the enzymes is very closely linked or allelic to the gene determining response to catabolite repression.