Isolation and characterization of stable hybrid mRNA molecules transcribed from ribosomal protein promoters in E. coli.

The promoters from the str and spc operons of ribosomal proteins from E. coli were inserted into the Hind II cleavage site of mini-Col E1 (pVH51) plasmid. For both promoters, strains with the hybrid plasmid accumulated a small RNA species not present in strains carrying the vector. These RNAs were analyzed by RNA sequencing techniques and compared to DNA sequences. In both cases, synthesis of the new RNA species is initiated by the cloned r protein promoter at the site predicted by previous in vitro experiments. The RNAs extend across the Hind II site used for cloning and terminate specifically in the vector sequences. The termination site was localized to six consecutive thymine nucleotides preceded by a sequence with dyad symmetry. We found that the RNA from the str promoter was 205 (+/- 3) nucleotides long and that from the spc promoter was 177 (+/- 3) nucleotides long. These "hybrid mRNAs" are much more stable than ordinary mRNA. The str hybrid mRNA has a half-life of about 8 min, and the spc hybrid mRNA has a half-life of about 18 min at 37 degrees C. These hybrid mRNAs provide an in vivo system with which to examine directly the discrete transcription products from ribosomal protein promoters, and to study promoter function and mRNA metabolism in vivo.