What is the role of the Shine-Dalgarno sequence in prokaryotic translation?

The Shine-Dalgarno sequence in prokaryotic translation serves as a ribosome binding site to initiate protein synthesis.

The Shine-Dalgarno (SD) sequence is a short, ribonucleic acid (RNA) sequence found in the 5' untranslated region (5' UTR) of prokaryotic messenger RNA (mRNA). It is named after its discoverers, Australian scientists John Shine and Lynn Dalgarno. This sequence is crucial in the process of translation, which is the synthesis of proteins from mRNA.

The SD sequence is typically located a few nucleotides upstream of the start codon (AUG) on the mRNA molecule. Its primary role is to serve as a binding site for the small subunit of the ribosome, which is the molecular machine that carries out protein synthesis. The sequence is complementary to a region on the 16S ribosomal RNA (rRNA) in the small subunit of the ribosome, allowing it to bind through base pairing.

Once the ribosome is bound to the mRNA at the SD sequence, it can then locate the start codon and begin the process of translation. The ribosome moves along the mRNA, decoding its sequence into the amino acid sequence of a protein. This process continues until the ribosome encounters a stop codon, at which point the newly synthesised protein is released.

The SD sequence is highly conserved, meaning it is similar across different species, highlighting its importance in the process of translation. However, the exact sequence can vary between different organisms and even between different mRNAs within the same organism. This variation can influence the efficiency of translation initiation, affecting the level of protein production.

In summary, the Shine-Dalgarno sequence plays a pivotal role in prokaryotic translation by acting as a binding site for the ribosome on the mRNA. This ensures the correct initiation of protein synthesis, a process fundamental to the survival and functioning of prokaryotic cells.