Convergent evolution of AUA decoding in bacteria and archaea.

Area of Science:

• Molecular Biology
• Genetics
• Evolutionary Biology

Background:

• The genetic code faces challenges in deciphering codons, such as AUA, which can ambiguously code for isoleucine (Ile) or methionine (Met).
• The universal genetic code typically assigns a single amino acid to each sense codon, with purine-ending codons (NNR) being particularly specific.

Purpose of the Study:

• To investigate the molecular mechanisms and evolutionary origins of AUA codon decoding in bacteria and archaea.
• To understand how modified nucleosides in tRNA anticodons enable specific amino acid assignment.

Main Methods:

• Comparative genomics and phylogenetic analysis to trace the evolutionary history of AUA decoding systems.
• Biochemical assays to characterize the function of modified tRNAs and their cognate aminoacyl-tRNA synthetases.
• Structural studies of modified nucleosides and their interactions within the ribosome.

Main Results:

• Bacteria utilize 2-lysylcytidine (L) and archaea use 2-agmatinylcytidine (agm(2)C) at the first position of tRNA(Ile) anticodons.
• These modifications prevent misreading of the AUG codon and ensure specific charging of tRNA(Ile) with Ile.
• Distinct biosynthetic pathways and enzymes for L and agm(2)C synthesis indicate independent evolutionary origins.

Conclusions:

• The analogous AUA decoding systems in bacteria and archaea arose through convergent evolution after their divergence from the last universal common ancestor (LUCA).
• This study provides insights into the adaptability of the genetic code and the diverse strategies employed by life to ensure translational fidelity.