First position wobble in codon-anticodon pairing: amber suppression by a yeast glutamine tRNA

Area of Science:

• Molecular Biology
• Genetics
• Yeast Biology

Background:

• Amber mutations are nonsense mutations that introduce premature stop codons.
• Transfer RNA (tRNA) molecules are crucial for protein synthesis, translating codons into amino acids.
• Saccharomyces cerevisiae (baker's yeast) is a model organism widely used in genetic research.

Purpose of the Study:

• To identify and characterize DNA fragments from Saccharomyces cerevisiae with suppressor activity.
• To elucidate the molecular mechanism by which a specific DNA fragment suppresses amber mutations.

Main Methods:

• DNA fragment isolation and subcloning from Saccharomyces cerevisiae.
• High copy number plasmid transformation and suppressor activity screening.
• DNA sequencing to identify genes within the active fragment.
• Site-directed mutagenesis (deletion) to confirm gene function.

Main Results:

• A 2.4-kb DNA fragment from yeast suppressed amber mutations when overexpressed.
• A 1.2-kb subclone retained suppressor activity, identified as a glutamine tRNA (tRNAGln) gene.
• Deletion of the tRNAGln gene abolished suppressor activity.
• The identified tRNAGln possesses an anticodon (CUG) capable of recognizing glutamine codons (CAG).

Conclusions:

• The identified yeast tRNAGln gene can suppress amber mutations (UAG) through inefficient translational readthrough.
• This readthrough mechanism likely involves codon-anticodon wobble at the first position.
• The study reveals a novel function for a specific tRNA in suppressing premature stop codons.