REGULATION OF RIBOSOMAL-PROTEIN SYNTHESIS IN ESCHERICHIA-COLI BY SELECTIVE MESSENGER-RNA INACTIVATION

In an E. coli strain lysogenic for .lambda.spc2 transducing phage, an extra copy of ribosomal protein (r-protein) genes in the spc and .alpha. operons are carried on the phage chromosome. Expression of genes in the spc operon in this merodiploid strain was compared with that in a control haploid strain carrying .lambda.trkA phage. The synthesis rate of spc mRNA, relative to other reference mRNA in the merodiploid strain, is about 2-fold higher than that in the control strain; yet, no dosage effect was observed in the synthesis rate of r-proteins in the spc or .alpha. operon. The spc mRNA was more rapidly degraded in the merodiploid strain than in the control strain, and its steady-state amount, relative to reference mRNA, was only slightly higher in the merodiploid strain than in the control strain. E. coli cells have the ability to regulate the rate of r-protein synthesis regardless of the rate of transcription of r-protein genes, presumably by inactivation of the mRNA followed by its degradation. A model is proposed which involves selective inactivation of r-protein mRNA by a feedback mechanism. The model can explain coordinated synthesis of r-proteins and other observations related to selective expression of certain alleles in diploid strains.