Protein factors (IFs, EFs, and eFs) play critical roles in each of the steps in translation of a message by the ribosome. Which of the following general statements pertaining to their functions and mechanisms of action is/are true?

A. Some of these factors bind tRNA and facilitate their binding to the appropriate sites in the ribosome.
B. Some of these factors bind GTP and rely on their hydrolysis to GDP to signal the correct interactions.
C. These factors are involved in initiation, elongation, and termination of translation.
D. Two of the above.
E. All of the above.

E. All of the above.

Explanation:

IF1 in prokaryotes is associated with the 30S subunit of the ribosome at the A site, thus preventing the entry of aminoacy-tRNA. Furthermore, it modulates the binding of IF2 to the ribosome by increasing its affinity. Another function is that it prevents the 50S subunit from sticking to the 30S subunit to create the 70S subunit. The IF2 and GTP complex binds to tRNA and thus controls the entry of tRNA into the ribosome. The GTP then hydrolyzes to GDP and Pi causing a change in conformation in IF2 causing IF2 to be released.

The small subunit needs IF3 to create the initiation complex, but it is released to facilitate its attachment to the 50S subunit. In the next step of translation, elongation factors play a major role. The prokaryotic elongation factor EF-Tu mediates the entry of aminoacyl-tRNA into the free site of the ribosome. The homolog in eukaryotes is the alpha subunit eEF1. EF-Ts acts as a guanine nucleotide exchange factor in the release of EF-Tu GDP from EF-Tu. The homolog in eukaryotes is the beta eEF1 and gamma subunits. EF-G is responsible for catalyzing the translocation of tRNA and mRNA by the ribosome at the end of each round in the elongation of the polypeptides. EF-P stimulates the conformation of peptide bonds. At the termination stage, release factors play a major role in identifying stop codons and polypeptide chain release. RF1 recognizes UAA and UAG stop codons, and RF2 recognizes UAA nad UGA stop codons. RF3 are class II release factors and aid in RF1 / 2 release in a GTP-dependent manner.