eIF2α interactions with mRNA control accurate start codon selection by the translation preinitiation complex.

Area of Science:

• Molecular Biology
• Protein Biochemistry
• Genetics

Background:

• Translation initiation is a critical step in gene expression, regulated by the preinitiation complex (PIC).
• The PIC undergoes conformational changes from an open to a closed state, influencing start codon recognition.
• eIF2α protein plays a key role in these conformational changes and start codon selection.

Purpose of the Study:

• To investigate the distinct roles of specific eIF2α arginines (R53, R55, R57) in regulating PIC conformation and translation initiation accuracy.
• To elucidate how interactions with mRNA and rRNA by eIF2α influence the stability of open and closed PIC states.

Main Methods:

• Site-directed mutagenesis of eIF2α arginines (R53, R55, R57).
• In vivo assays measuring translation initiation at specific start codons (HIS4, SUI1, GCN4).
• In vitro biochemical assays to assess ternary complex (TC) binding and dissociation from PICs.

Main Results:

• R55/R57 substitutions destabilized the closed PIC, reducing recognition of UUG and poor-context AUG start codons.
• R53 substitution destabilized the open PIC, enhancing initiation at UUG and poor-context AUGs while reducing TC loading.
• Distinct interactions of eIF2α with mRNA (closed complex) and rRNA (open complex) were identified.

Conclusions:

• Specific eIF2α arginines mediate distinct interactions that stabilize open and closed PIC conformations.
• These conformational changes are crucial for accurate start codon selection during translation initiation in vivo.
• Understanding these mechanisms provides insights into gene expression regulation and potential therapeutic targets.