Relationship between size of mRNA ribosomal binding site and initiation factor function.

Area of Science:

• Molecular Biology
• Biochemistry
• Genetics

Background:

• Initiation factor 3 (IF3) plays a crucial role in bacterial translation initiation.
• IF3's interaction with ribosomal subunits and mRNA influences the selection of the start codon.
• The precise mechanism of IF3's regulatory role, particularly concerning mRNA length, requires further elucidation.

Purpose of the Study:

• To investigate the effect of mRNA template length on IF3's modulation of initiator tRNA binding to the 30S ribosomal subunit.
• To determine the specific lengths of 5' and 3' extensions on AUG triplets that alter IF3's inhibitory or stimulatory behavior.
• To understand the role of template length in IF3-mediated selection of the mRNA initiation region.

Main Methods:

• Studied the binding of fMet-tRNA(fMet) to 30S ribosomal subunits using AUG triplets and poly(AUG) templates.
• Utilized AUG triplets extended with homo-oligonucleotides of varying lengths on the 5' and 3' sides.
• Assessed both equilibrium binding and initial rates of ternary complex formation.

Main Results:

• IF3 inhibited fMet-tRNA binding with short AUG templates but stimulated it with poly(AUG).
• At equilibrium, IF3 inhibition was abolished when AUG was extended by at least 10 nucleotides (5') or 35-40 nucleotides (3').
• For initial rates, shorter extensions (4 nucleotides 5', 20-30 nucleotides 3') were sufficient for IF3 stimulation.

Conclusions:

• The length of the mRNA template significantly influences IF3's regulatory function in translation initiation.
• IF3's dual role (inhibition/stimulation) is dependent on the mRNA's interaction with the ribosome, likely related to initiation site selection.
• These findings provide insights into the intricate mechanism of how ribosomes select the correct mRNA initiation region with the help of initiation factors.