Ribosome Binding Site
<p><b>A ribosome binding site, or ribosomal binding site (RBS)</b>, is a sequence of nucleotides upstream of the start codon of an mRNA transcript that is responsible for the recruitment of a ribosome during the initiation of protein translation. Mostly, RBS refers to bacterial sequences, although internal ribosome entry sites (IRES) have been described in mRNAs of eukaryotic cells or viruses that infect eukaryotes. Ribosome recruitment in eukaryotes is generally mediated by the 5' cap present on eukaryotic mRNAs.</p>
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<b>Prokaryotes</b>
The RBS in prokaryotes is a region upstream of the start codon. This region of the mRNA has the consensus 5'-AGGAGG-3', also called the Shine-Dalgarno (SD) sequence. The complementary sequence (CCUCCU), called the anti-Shine-Dalgarno (ASD) is contained in the 3’ end of the 16S region of the smaller (30S) ribosomal subunit. Upon encountering the Shine-Dalgarno sequence, the ASD of the ribosome base pairs with it, after which translation is initiated.
Variations of the 5'-AGGAGG-3' sequence have been found in Archaea as highly conserved 5′-GGTG-3′ regions, 5 basepairs upstream of the start site. Additionally, some bacterial initiation regions, such as rpsA in E.coli completely lack identifiable SD sequences.</p>
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<b>Eukaryotes</b>
Ribosome recruitment in eukaryotes happens when eukaryote initiation factors elF4F and poly(A)-binding protein (PABP) recognize the 5' capped mRNA and recruit the 43S ribosome complex at that location.
Translation initiation happens following recruitment of the ribosome, at the start codon (underlined) found within the Kozak consensus sequence ACCAUGG. Since the Kozak sequence itself is not involved in the recruitment of the ribosome, it is not considered a ribosome binding site.
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Internal ribosome entry site (IRES)</b>
Eukaryotic ribosomes are known to bind to transcripts in a mechanism unlike the one involving the 5' cap, at a sequence called the internal ribosome entry site. This process is not dependent on the full set of translation initiation factors (although this depends on the specific IRES) and is commonly found in the translation of viral mRNA.</p>
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<img src="/cf3a4868-8836-5d44-a9c5-22ae7f4e0819.png"/> <img src="/881be874-1683-50e0-ae9b-93578b35c3f6.png"/> </p>
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See IGEM website opposite</p>
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