Evolving Mistranslating tRNAs Through a Phenotypically Ambivalent Intermediate in Saccharomyces cerevisiae.

Area of Science:

• Molecular Biology
• Genetics
• Evolutionary Biology

Background:

• The genetic code, which translates nucleic acids to proteins, was traditionally considered immutable.
• However, natural variations in the genetic code can confer selective advantages.
• Understanding these variations is key to comprehending evolutionary mechanisms.

Purpose of the Study:

• To detect mistranslation and identify mechanisms driving genetic code evolution.
• To investigate how transfer RNA (tRNA) mutations can lead to altered genetic coding.
• To explore the evolutionary potential of seemingly deleterious genetic code changes.

Main Methods:

• Utilized a sensitive selection system in *Saccharomyces cerevisiae* to identify mistranslating tRNA variants.
• Focused on suppressing a deleterious allele (tti2-L187P) to detect functional tRNA mutations.
• Characterized specific tRNA^Ser_UGG variants (G26A and G9A) through growth assays, heat shock response analysis, and in vitro studies.

Main Results:

• Identified four tRNA^Ser_UGG variants and mistranslating tRNA^Leu_UGG variants that allow mistranslation at tolerable levels.
• Characterized two tRNA^Ser_UGG variants: G26A (reduced growth, heat shock response, degraded via rapid tRNA decay) and G9A (minimal growth impact, stable, altered aminoacylation and folding).
• Found that G26A and G9A mutations were phenotypically neutral in a wild-type tRNA context, suggesting ambivalent intermediates in evolution.

Conclusions:

• Proposed a model for genetic code evolution involving tRNA anticodon mutations and mistranslation.
• These variations can arise through phenotypically ambivalent intermediates that reduce tRNA function.
• This provides insight into how the genetic code can adapt and evolve over time.