Structural analysis of an eIF3 subcomplex reveals conserved interactions required for a stable and proper translation...

Area of Science:

• Molecular Biology
• Structural Biology
• Yeast Genetics

Background:

• The eukaryotic translation initiation factor 3 (eIF3) is crucial for protein synthesis initiation.
• The precise structural organization and function of eIF3 subunits, particularly their interactions, remain incompletely understood.

Purpose of the Study:

• To elucidate the structural basis of eIF3 complex assembly and its role in translation initiation.
• To investigate the function of the eIF3i/TIF34 and eIF3b/PRT1 interaction in vivo.

Main Methods:

• X-ray crystallography to determine the 2.2 Å resolution structure of the eIF3i/TIF34 and eIF3b/PRT1 complex.
• Site-directed mutagenesis to analyze the functional importance of conserved interactions.
• In vivo studies in yeast to assess growth defects and subunit association.

Main Results:

• The crystal structure reveals conserved interactions between yeast eIF3i/TIF34 and the eIF3b/PRT1 C-terminus.
• Mutations disrupting these interactions cause severe growth defects and destabilize eIF3 and 40S subunit association.
• Aberrant pre-initiation complexes (PICs) form, impairing mRNA scanning and AUG recognition, which is partially rescued by eIF3g/TIF35 or eIF1 overexpression.

Conclusions:

• The eIF3b/PRT1 C-terminus is essential for the co-operative recruitment of eIF3i/TIF34 and eIF3g/TIF35 to the 40S subunit.
• This recruitment is critical for the stable assembly of 48S PICs and accurate start codon selection.
• Understanding these interactions provides insights into the regulation of translation initiation in eukaryotes.