Although the ShineDalgarno sequences vary they include examp

Although the Shine-Dalgarno sequences vary, they include examples like GAGGGG that could serve as code (in this case, Glu-Gly). Does this imply that the sequence Glu-Gly cannot ever occur in a protein, because it would be read as a Shine-Dalgarno sequence?

Solution

The start codon in prokaryotes is fMet and in eukaryotes, it is, Met. Both the prokaryotes and eukaryotes find different signals to identify the start codons. In prokaryotes, the initiation codon in mRNA is preceded by Shine-Delgarno sequences to which the complementary base pairs bind near the 3’ end terminus of the 16S ribosomal RNA.

This results in the initiation of the translation at both the 5’ end and the internal initiation sites. Once the initiation occurs, it does not occur again, such as in the middle of the sequence. Reading of a initiation codon is different from reading the amino acid coding sequence, thus, Glu-Gly do occur in a protein. .