Question

Although the RBS, Ribosome-Binding Site, sequences vary considerably in different genes, they include examples like GAGGGG that could serve as code for Glu-Gly. Does this imply that the amino acid sequence Glu-Gly can never occur in protein, lest it be read as a RBS sequence? Explain.

Answer 1

Although the RBS, Ribosome-Binding Site, sequences vary considerably in different genes, they include examples like GAGGGG that could serve as code for Glu-Gly. Does this imply that the amino acid sequence Glu-Gly can never occur in protein, lest it be read as a RBS sequence? Explain.

Firstly I want to explain you what is ribosome binding site, so that it will make clear cut concept in your mind.

A ribosome binding site (RBS) located upstream of the start codon of an mRNA and is responsible for the positioning of ribosome for initiation of protein translation.

For example, Shine-Dalgarno (SD) Sequence is a ribosomal binding site in in bacteria, archaea, chloroplast and mitochondrial mRNA. It is located around 8 bases upstream of the start codon AUG. It helps in recruitment of the ribosome to the messenger RNA (mRNA) for initiation of protein synthesis by putting the ribosome with the start codon.

The start codon is AUG codes N-formylmethionine amino acid for initiation of translation process.

Now our question is that RBS can never occur in protein, lest it be read as a RBS sequence.

I will give you answer by giving example of Shine-Dalgarno sequence which is RBS.
This AUG codon when attached to Shine-Dalgarno sequence is read differently when it is compared to the codon which encodes methionine in the middle of the mRNA sequence.

AUG codon has dual function such as it codes for the amino acid methionine( Met) and it also acts as an initiator codon ( fMet).

If a ribosome is not translating, then an AUG with the appropriate nucleotide context such as Shine-Dalgarno in prokaryotes and Kozak in eukaryotes will trigger the initiation of translation with N-formyl methionine (prokaryotes) or methionine (eukaryotes). If a ribosome is elongating a polypeptide, then AUG always codes for methionine. This is the answer to your question. Hope it is clear to you....
Thanks