Structural basis of AUC codon discrimination during translation initiation in yeast

Area of Science:

• Molecular Biology
• Structural Biology
• Genetics

Background:

• Eukaryotic translation initiation involves the 48S preinitiation complex (PIC) scanning mRNA 5' UTRs for start codons.
• Accurate start codon recognition is vital, with near-cognate codons being rejected.

Purpose of the Study:

• To elucidate the structural mechanisms underlying the discrimination of near-cognate start codons by the 48S PIC.
• To understand how the PIC differentiates between cognate (AUG) and near-cognate (e.g., AUC) codons.

Main Methods:

• Cryo-electron microscopy (Cryo-EM) to capture yeast 48S PICs bound to near-cognate codons.
• Structural analysis of codon-anticodon interactions and eukaryotic initiation factor (eIF) dynamics.

Main Results:

• Near-cognate AUC codon binding induces instability in the P-site codon-anticodon interaction.
• This instability leads to a disordered eIF1A N-terminal tail and impaired eIF5 binding.
• Metastable states of the eIF2 ternary complex and a swivelled 48S PIC conformation are observed, crucial for discrimination.

Conclusions:

• The structural dynamics of the 48S PIC, particularly involving eIF1A, eIF5, and eIF2, are critical for near-cognate codon rejection.
• A swivelled head conformation of the 48S PIC is essential for accurate codon-anticodon selection during translation initiation.