Ribosomal binding site
A ribosomal binding site (RBS) is a sequence on mRNA that is bound by the ribosome when initiating protein translation. In eukaryotes it is the 5' cap of the messenger RNA, in prokaryotes it is a region called the Shine-Dalgarno sequence 6-7 nucleotides upstream of a start codon. Additionally viruses can have internal ribosome entry sites (IRES) within an mRNA transcript. Once the ribosome has bound, it recruits initiation factors and begins the translation process.
The prokaryotic ribosome binds a region 6-7 nucleotides upstream of the start codon (called the Shine-Dalgarno sequence). The sequence is complementary to the 3' end of the rRNA. The ribosome searches for this site and binds to it through base-pairing of nucleotides.
An internal ribosome entry site (IRES) in viruses allows the eukaryotic ribosome to bind within the mRNA rather than being restricted to the 5' cap. It acts similarly to the prokaryotic Shine-Dalgarno sequence.
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