Post-transcriptional regulatory mutants in a ribosomal protein-RNA polymerase operon of E. coli

A high copy number plasmid that carries the promoter PJ, intact rplJ and a deletion of the 3' terminal portion of rplL is detrimental to the growth of the host bacterium. Six independent point mutations on the plasmid that overcome this detriment have been isolated. Nucleotide sequence analysis demonstrates that all six mutants are single base pair alterations, occur within the leader region of the rplJ operon and are well removed from the presumed position of the primary promoter, PJ. These mutant plasmids exhibit normal transcription of rplJ-rplL but do not translate rplJ messenger RNA to yield plasmid-specified L10 ribosomal protein. We suggest that these mutations define a regulatory region within the leader sequence of the RNA transcript that serves to modulate the translational efficiency of rplJ messenger RNA.