Localization of the target site for translational regulation of the L11 operon and direct evidence for translational coupling in Escherichia coli.

The L11 ribosomal protein operon in Escherichia coli consists of the structural genes for proteins L11 and L1. Hybrid deletion plasmids were constructed carrying these two genes with decreasing amounts of the leader mRNA under lac transcriptional control. Measurements of mRNA and protein synthesis directed by these plasmids in vitro and in vivo demonstrate that the regulation of this operon is posttranscriptional and identifies a region of the mRNA, preceding the proximal L11 gene, important for successful feedback inhibition of L11 and L1 synthesis by L1. Additionally, deletions extending to the ribosome binding site of the L11 gene fail to synthesize both L11 and the downstream L1 protein although synthesis of the corresponding mRNA remains unchanged. These results directly demonstrate the presence of translational coupling in this bicistronic operon.