The new classification scheme of the genetic code, its early evolution, and tRNA usage

Area of Science:

• Genetics
• Molecular Biology
• Evolutionary Biology

Background:

• The standard genetic code classification lacks explicit representation of inherent symmetries.
• Understanding these symmetries is crucial for deciphering the code's evolutionary history.

Purpose of the Study:

• To propose a new classification scheme for the genetic code that highlights five distinct symmetries.
• To investigate the reflection of these genetic code symmetries in tRNA gene usage patterns across diverse organisms.
• To provide evidence supporting theories on the early evolution of the genetic code.

Main Methods:

• Developed a novel classification scheme for the genetic code based on five symmetries.
• Analyzed tRNA gene counts from 16 archaea, 81 bacteria, and 7 eukaryotes.
• Correlated genetic code symmetries with observed tRNA usage patterns.

Main Results:

• The new classification reveals codon-anticodon, codon-reverse codon, sense-antisense, purine-pyrimidine, and keto-aminobase symmetries.
• Reverse stop codons largely lack dedicated tRNAs, with a notable exception in humans.
• A** anticodons exhibit significant suppression in tRNA gene usage.
• Identified tRNA usage patterns align with hypotheses of early genetic code evolution.

Conclusions:

• The proposed genetic code classification effectively highlights underlying symmetries.
• Observed tRNA usage patterns provide empirical support for evolutionary hypotheses of the genetic code.
• Findings suggest pre-tRNAs may have possessed bidirectional codon-binding capabilities.