ribosomebinding

Ribosome binding is the initial association of ribosomal subunits with messenger RNA during translation initiation. This step is required to recruit the ribosome to the mRNA, establish the correct reading frame, and begin polypeptide synthesis. The general principle is conserved across life, but the molecular details differ between prokaryotes and eukaryotes.

In bacteria, the small 30S subunit recognizes the ribosome binding site, typically a Shine-Dalgarno sequence located upstream of the start codon. Base pairing between the 16S rRNA anti-Shine-Dalgarno sequence and the mRNA RBS aligns the start codon in the P site. Initiation factors IF1, IF2, and IF3 assist in this assembly, and GTP hydrolysis promotes joining of the 50S subunit to form the 70S initiation complex.

In eukaryotes, ribosome binding is cap-dependent. The 40S subunit, in association with initiation factors, binds to the 5' cap of the mRNA and scans the 5' untranslated region until a start codon within a favorable context, often described by the Kozak sequence. Upon start codon recognition, the 60S subunit joins to produce the 80S initiation complex.

Factors influencing ribosome binding include mRNA secondary structure that can occlude or expose the ribosome binding site, regulatory RNA elements such as riboswitches and small RNAs, RNA-binding proteins, and sequence context around the start codon. Environmental conditions and cellular physiology also modulate translation initiation efficiency and ribosome occupancy.

Ribosome binding is a key control point in gene expression and is exploited in biotechnology and medicine. Understanding and predicting binding efficiency aids in gene design, while antibiotics and other compounds can disrupt initiation by interfering with ribosome-mRNA interactions.