Conformational selection of translation initiation factor 3 signals proper substrate selection

Area of Science:

• Molecular Biology
• Biochemistry
• Structural Biology

Background:

• Initiation factor 3 (IF3) is crucial for regulating translation initiation fidelity.
• IF3 binds the small (30S) ribosomal subunit, influencing initiator tRNA and mRNA selection.
• The precise mechanism of IF3 in signaling correct substrate selection is not fully understood.

Purpose of the Study:

• To elucidate the molecular mechanism by which IF3 promotes accurate substrate selection during translation initiation.
• To investigate the conformational dynamics of IF3 within the 30S initiation complex (30S IC).

Main Methods:

• Single-molecule fluorescence resonance energy transfer (smFRET) was employed.
• The conformational states of IF3 bound to the 30S IC were analyzed.

Main Results:

• Escherichia coli IF3 exists in a dynamic equilibrium of at least three conformations when bound to the 30S IC.
• A correct anticodon-codon interaction between initiator tRNA and the start codon selectively shifts IF3 to a single conformation.
• This conformational shift occurs within a fully assembled 30S IC.

Conclusions:

• The findings support a conformational selection model for IF3 function.
• IF3's specific conformation, stabilized by correct substrate binding, facilitates subsequent steps in translation initiation.
• This mechanism ensures the fidelity of the translation start process.