Differential translation of the genes encoding the proton-translocating ATPase of Escherichia coli.

Translation of the gene for the b subunit of the Escherichia coli proton-translocating ATPase has been examined. Oligonucleotide-directed site-specific mutagenesis was used to mutate certain nucleotides in the intergenic region between uncE (c) and uncF (b). One of the changes was predicted to lower the stability of a proposed stem structure which blocked the ribosome binding site of the uncF mRNA segment. The result of the mutation is a nearly 3-fold increase in the rate of synthesis of the b polypeptide. Another mutation was introduced which changed the initiation codon for uncF from GUG to AUG. This change resulted in an approximately 2-fold increase in the synthesis rate of the b polypeptide. These results suggest that secondary structure in the mRNA and the use of a less efficient initiation codon play a role in restricting translation initiation of the uncF mRNA segment. These mechanisms may, in part, explain how the polypeptides of the ATPase complex are synthesized in approximately the same relative amounts as they appear in the assembled complex.