Discrimination between defects in elongation fidelity and termination efficiency provides mechanistic insights into...

Area of Science:

• Molecular Biology
• Genetics
• Biochemistry

Background:

• Translational readthrough, the suppression of stop codons, arises from impaired translation elongation accuracy or termination efficiency.
• Previous research lacked methods to differentiate the contributions of elongation versus termination to readthrough phenotypes.
• Understanding these distinct processes is crucial for evaluating how translational machinery defects affect termination.

Purpose of the Study:

• To develop and utilize combined reporter systems to discern the mechanisms underlying translational readthrough in Saccharomyces cerevisiae.
• To investigate the specific contributions of translation elongation fidelity and termination efficiency to the readthrough process.
• To assess how alterations in ribosomal components influence these distinct translational events.

Main Methods:

• Developed a misincorporation reporter system using firefly luciferase gene with near-cognate mutations to monitor elongation errors.
• Quantified elongation fidelity by measuring luciferase activity from a missense-inactivated mutant allele.
• Employed a readthrough reporter system in conjunction with the misincorporation reporter to analyze both elongation and termination.
• Investigated the effects of paromomycin, mutant ribosomal protein S9B expression, and ribosomal protein L12 depletion.

Main Results:

• Paromomycin stimulated luciferase activity in only a subset of mutant proteins, indicating limited induction of elongation errors by this aminoglycoside.
• A similar bias in near-cognate misreading was observed upon expression of mutant ribosomal protein S9B or depletion of ribosomal protein L12.
• The combined reporter systems demonstrated that different ribosomal regions differentially affect elongation fidelity and termination efficiency.

Conclusions:

• The study successfully differentiated the contributions of translation elongation and termination to translational readthrough.
• Ribosomal protein alterations and specific chemical agents exhibit distinct effects on translation fidelity and termination.
• This work provides a framework for dissecting the complex interplay between ribosomal function, elongation accuracy, and termination efficiency.