The mechanism of histidase induction and formation in Bacillus subtilis

The role of the inducer, L-histidine, in the synthesis of histidase (L-histidine ammonia lyase, B.C. 4.3.1.3) in Bacillus subtilis was investigated. It was found that induced cells poisoned with actinomycin, an inhibitor of RNA synthesis, lose their capacity for the formation of a protein precursor of histidase at a rate which is independent of the presence or absence of the inducer. These results show that the inducer does not increase the intracellular level of histidase-specific messenger RNA by preventing the destruction of the major portion of this material, the fraction that is engaged in protein synthesis. The possibility has not been excluded that the inducer exerts its effect by bringing about the stabilization of the messenger RNA that is still attached to DNA or has not yet become attached to ribosomes. Alternatively, the inducer may actually stimulate the synthesis of histidase-specific messenger RNA. The conversion of the precursor to active enzyme appears to involve polymerization of monomers, rather than the release of ribosome-bound inactive enzyme.