Release factor

A release factor is a protein that allows for the termination of translation by recognizing the termination codon or stop codon in an mRNA sequence.

During translation of mRNA, most codons are recognized by "charged" tRNA molecules, called aminoacyl-tRNAs because they are adhered to specific amino acids corresponding to each tRNA's anticodon.

In the standard genetic code, there are three mRNA stop codons: UAG ("amber"), UAA ("ochre"), and UGA ("opal" or "umber").

Although these stop codons are triplets just like ordinary codons, they are not decoded by tRNAs. It was discovered by Mario Capecchi in 1967 that, instead, tRNAs do not ordinarily recognize stop codons at all, and that what he named "release factor" was not a tRNA molecule but a protein. Later, it was demonstrated that different release factors recognize different stop codons.

Prokaryotic translation termination is mediated by three prokaryotic release factors: RF1, RF2, and RF3.

Likewise, eukaryotic translation termination involves two eukaryotic release factors: eRF1 and eRF3.

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