Translational coupling at the intercistronic boundary of an artificially constructed operon in Escherichia coli.

By using recombinant DNA techniques an artificial operon was constructed that codes for two fusion proteins under the control of the beta-lactamase promoter of plasmid pBR322. The two proteins are: 1. beta-lactamase-trp B (43 kd) 2. trpA-beta-galactosidase (120 kd). Frameshift mutations in the N-terminal region of the first gene resulted in a dramatic reduction in the synthesis of the protein coded by the second gene. This strong polar effect could not be accounted for by correspondingly lower level of the distal region of the messenger RNA, only by "translational coupling" due to the overlap of the termination codon of the first gene with the initiation codon of the second gene. It was concluded that the strong "translational coupling" observed in this artificial operon can be generally used to ensure coordinated high-level synthesis of proteins in operons constructed by recombinant DNA techniques.