On the role of the Shine-Dalgarno sequence in determining the efficiency of translation initiation at a weak start codon in the car operon of Escherichia coli K12.

Translation of the carA gene is efficiently initiated at the intrinsically weak UUG codon. A single nucleotide substitution changing the Shine-Dalgarno box of carA (GGAGG) into the sequence TGAGG reduces translation of carA sevenfold. This result supports the view that extensive complementarity between the Shine-Dalgarno sequence and 16S RNA contributes significantly to the efficiency of translation when the latter starts at a weak initiation triplet.