Shine-Dalgarno (S-D) sequence

An eight nucleotide concensus sequence 5' UAAGGAGG 3' found in bacterial mRNAs five to ten bases before the translation initiation codon (AUG). It is thought to be involved in initiation of translation by helping the mRNA bind to the ribosome (16S rRNA), thus it can be called the ribosomal binding site (see also Kozak sequence). In eukaryotic DNA, there is no such sequence. The 5' cap present on all eukaryotic mRNAs seems to be the first signal to start protein synthesis.