Start codon-associated ribosomal frameshifting mediates nutrient stress adaptation.

Area of Science:

• Molecular Biology
• Genetics
• Proteomics

Background:

• The canonical model posits ribosomes strictly adhere to the reading frame set by the start codon during translation.
• Unannotated mass spectrometry spectra in the human proteome suggest uncharacterized protein variants or translation events.

Purpose of the Study:

• To investigate the phenomenon of out-of-frame translation occurring immediately after the start codon.
• To identify mechanisms and regulatory factors governing reading frame fidelity during translation initiation.
• To explore the biological significance of such translational events, particularly under nutrient stress.

Main Methods:

• Super-resolution ribosome profiling to visualize translation dynamics at single-ribosome resolution.
• Massively parallel reporter assays to screen for sequence elements influencing ribosomal frameshifting.
• Biochemical assays to assess the role of eukaryotic initiation factor 5B (eIF5B) in reading frame maintenance.
• Investigating the impact of amino acid starvation on ribosomal frameshifting and eIF5B levels.

Main Results:

• Pervasive out-of-frame translation, termed start codon-associated ribosomal frameshifting (SCARF), occurs immediately from the start codon.
• Specific sequence elements were identified as enhancers or repressors of SCARF, indicating regulation of reading frame fidelity.
• The eukaryotic initiation factor 5B (eIF5B) was found to stabilize initiating ribosomes and maintain reading frame fidelity.
• Amino acid starvation induces SCARF through proteasomal degradation of eIF5B, linking translational noise to stress response.

Conclusions:

• Ribosomal frameshifting at the start codon is a widespread phenomenon, challenging the canonical model of translation.
• SCARF is regulated by sequence elements and protein factors like eIF5B, which plays a crucial role in maintaining reading frame fidelity.
• Stress-induced SCARF, mediated by eIF5B loss, contributes to cellular adaptation during nutrient starvation by enabling amino acid recycling and selective mRNA translation.
• Translational 'noise' can have beneficial roles in cellular adaptation to environmental stress.