Protein synthesis by long-lived messenger ribonucleic acid in bacteria.

1. Experiments were performed to investigate two hypotheses about the function of long-lived messenger RNA in bacteria. After RNA synthesis had been stopped by the addition of actinomycin, continuing protein synthesis was used as a measure of persistent messenger RNA. 2. The hypothesis that messenger RNA responsible for the synthesis of membrane protein is exceptionally long-lived was tested in experiments with protoplasts of Bacillus megaterium. However, this messenger RNA proved to be of approximately average stability. 3. The hypothesis that long-lived messenger RNA is responsible for the synthesis of constitutive proteins was tested by comparing the synthesis of penicillinase in an inducible and a constitutive strain of Bacillus licheniformis. After the addition of actinomycin, penicillinase synthesis continued for far longer in the constitutive than in the inducible strain. This difference is attributed to a difference in stability of the penicillinase-messenger RNA in the two strains, which does not extend to all messenger RNA indiscriminately. 4. A model is tentatively proposed to account for the altered stability of messenger RNA in the constitutive mutant.