Both prokaryotes and eukaryotes use additional protein factors, called initiation and termination factors, to help begin and end translation.

Initiation factors, found in both prokaryotes (known as IF-1, IF-2, and IF-3) and eukaryotes (known as eIF-1, eIF-2, eIF-3 and eIF-4 ) are the proteins that help in the initiation of translation. These factors help to bring an mRNA, initiator tRNA, and ribosome into proper alignment. In eukaryotes, energy is used during the initiation process in the form of GTP hydrolysis.

Release factors, on the other hand, are the termination cofactors that end the process of translation when a stop codon is reached at the aminoacyl site (A site) of the ribosome. Different release factors release different stop codons. When a stop codon is reached, a release factor binds with the ribosome instead of a new tRNA, ending translation.

Practice Questions

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Practice Exam 4 C/P Section Passage 5 Question 24

Key Points

• The initiation factors IF in prokaryotes and eIF in eukaryotes help to bring the mRNA, tRNA and ribosomes at the peptidyl site (P site) of the ribosome to initiate translation.

• The termination factors or release factors bind with ribosomes instead of a new tRNA when a stop codon is reached at the aminoacyl site (A site).

Key Terms

Initiation factors: Proteins that help initiate translation by forming the pre-initiation complex with the initiator tRNA and ribosome.

Release factors: Proteins that help end translation by recognizing and binding a stop codon at the aminoacyl site of a ribosome in place of a new tRNA.