A computational screen for alternative genetic codes in over 250,000 genomes

Area of Science:

• Genetics
• Evolutionary Biology
• Bioinformatics

Background:

• The genetic code was historically considered a 'frozen accident,' suggesting limited evolutionary potential.
• Previous discoveries of alternative genetic codes were largely anecdotal, hindering broad conclusions on evolutionary patterns.
• Understanding codon reassignment evolution requires systematic analysis of diverse genetic codes.

Purpose of the Study:

• To computationally predict amino acid decoding for each codon from nucleotide sequence data.
• To systematically survey genetic code usage across a large dataset of bacterial and archaeal genomes.
• To identify and characterize novel instances of genetic code evolution and codon reassignment.

Main Methods:

• Development of Codetta, a computational tool for predicting codon decoding.
• Analysis of over 250,000 bacterial and archaeal genome sequences from GenBank.
• Identification of new codon reassignments, particularly involving arginine codons.

Main Results:

• Discovery of five new codon reassignments in bacteria, including sense codon changes for arginine codons (AGG, CGA, CGG).
• Identification of AGG reassignment to methionine in uncultivated Bacilli, likely driven by tRNA amino acid charging.
• Association of CGA and/or CGG reassignment with low GC content genomes, suggesting a role for this evolutionary force.

Conclusions:

• The genetic code exhibits greater evolutionary flexibility than previously assumed.
• Codon reassignment is an ongoing evolutionary process in bacteria and archaea.
• Specific evolutionary pressures, such as GC content and tRNA modifications, can drive genetic code evolution.