Release factor
Encyclopedia
A release factor is a protein
that allows for the termination of translation by recognizing the termination codon or stop codon in a mRNA sequence.
During translation of mRNA, most codons are recognized by "charged" tRNA molecules, called aminoacyl-tRNA
s because they are adhered to specific amino acid
s 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. Instead, it was discovered by Mario Capecchi
in 1967 that 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 release factors: RF1 RF2 and RF3.
Eukaryotic translation termination similarly involves two release factors: eRF1 and eRF3.
Protein
Proteins are biochemical compounds consisting of one or more polypeptides typically folded into a globular or fibrous form, facilitating a biological function. A polypeptide is a single linear polymer chain of amino acids bonded together by peptide bonds between the carboxyl and amino groups of...
that allows for the termination of translation by recognizing the termination codon or stop codon in a mRNA sequence.
During translation of mRNA, most codons are recognized by "charged" tRNA molecules, called aminoacyl-tRNA
Aminoacyl-tRNA
Aminoacyl-tRNA is tRNA to which its cognated amino acid is adhered. Its role is to deliver the amino acid to the ribosome where it will be incorporated into the polypeptide chain that is being produced...
s because they are adhered to specific amino acid
Amino acid
Amino acids are molecules containing an amine group, a carboxylic acid group and a side-chain that varies between different amino acids. The key elements of an amino acid are carbon, hydrogen, oxygen, and nitrogen...
s corresponding to each tRNA's anticodon.
In the standard genetic code
Genetic code
The genetic code is the set of rules by which information encoded in genetic material is translated into proteins by living cells....
, 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. Instead, it was discovered by Mario Capecchi
Mario Capecchi
Mario Renato Capecchi is an Italian-born American molecular geneticist and a co-winner of the 2007 Nobel Prize in Physiology or Medicine for discovering a method for introducing homologous recombination in mice employing embryonic stem cells, with Martin Evans and Oliver Smithies...
in 1967 that 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 release factors: RF1 RF2 and RF3.
- RF1 recognizes the termination codons UAA and UAG
- RF2 recognizes UAA and UGA
- RF3 is a GTP-binding protein that facilitates the binding of RF1 and RF2 to the ribosomal complex
Eukaryotic translation termination similarly involves two release factors: eRF1 and eRF3.
- eRF1 recognizes all three termination codons
- eRF3 is a ribosome-dependent GTPase that helps eRF1 release the completed polypeptide