Functional elements in initiation factors 1, 1A, and 2β discriminate against poor AUG context and non-AUG start...

Area of Science:

• Molecular Biology
• Genetics
• Biochemistry

Background:

• The yeast gene SUI1, encoding eukaryotic translation initiation factor 1 (eIF1), possesses a suboptimal context start codon.
• This suboptimal context suggests a potential for translational autoregulation of eIF1 levels.
• Previous studies identified mutations affecting translation initiation at non-AUG codons (Sui(-) and Ssu(-) phenotypes).

Purpose of the Study:

• To investigate whether eIF1 discriminates against AUG start codons in suboptimal contexts.
• To determine the role of specific residues in eIF1, eIF1A, and eIF2β in this discrimination process.
• To elucidate the mechanism of translational autoregulation of SUI1 expression.

Main Methods:

• Analysis of yeast strains with mutations in eIF1, eIF1A, and eIF2β.
• Comparison of SUI1 gene expression with native and optimal context start codons.
• Phenotypic characterization of Sui(-) and Ssu(-) mutations in relation to start codon context.

Main Results:

• Sui(-) mutations in eIF1, eIF1A, and eIF2β increased SUI1 expression, an effect reduced by optimizing the start codon context.
• Ssu(-) mutations in eIF1 and eIF1A decreased SUI1 expression specifically with the native, suboptimal context.
• Specific residues in eIFs 1, 1A, and 2β are crucial for discriminating against weak start codon contexts and non-AUG codons.

Conclusions:

• Discrimination against suboptimal AUG contexts by eIFs is a conserved mechanism for regulating translation initiation.
• Context nucleotides and the AUG start codon cooperate to stabilize the preinitiation complex.
• While eIF1 autoregulates via context discrimination, it does not entirely prevent eIF1 overproduction, explaining the hyperaccuracy phenotype of SUI1 overexpression.