Ribosomal A-site interactions with near-cognate tRNAs drive stop codon readthrough

Area of Science:

• Molecular Biology
• Genetics
• Biochemistry

Background:

• Transfer RNAs (tRNAs) are central to protein synthesis, translating messenger RNA (mRNA) codons into amino acids.
• Beyond canonical translation, tRNAs participate in specialized processes like programmed stop codon readthrough (SC-RT).
• Efficient SC-RT requires tRNAs to compete with release factors at stop codons, allowing translation to proceed.

Purpose of the Study:

• To investigate the structural determinants of tRNA anticodon stems (AS) that govern efficient programmed stop codon readthrough (SC-RT).
• To understand how tRNA-ribosome interactions influence the fidelity and efficiency of translation termination evasion.

Main Methods:

• Comparative analysis of tRNA structures and function in Saccharomyces cerevisiae and Trypanosoma brucei.
• Investigating interactions between tRNA anticodon stems and ribosomal proteins (Rps30/eS30, Rps25/eS25) in the ribosomal decoding site.
• Correlating anticodon stem length and definition with SC-RT efficiency across different organisms.

Main Results:

• tRNAs promoting efficient SC-RT establish specific contacts between their anticodon stem (AS) and ribosomal proteins Rps30/eS30 and Rps25/eS25.
• The length and structural integrity of the AS are critical for the strength of these interactions.
• These findings are conserved and observable in organisms with altered stop codon usage.

Conclusions:

• The anticodon stem's structural properties directly influence tRNA's ability to mediate stop codon readthrough.
• This mechanism highlights a novel aspect of tRNA biology and ribosome-ribosome interactions.
• Findings provide a basis for designing artificial tRNAs with tailored decoding capabilities.