Primordial reading of genetic information

Area of Science:

• Molecular Biology
• Evolutionary Biology
• Genetics

Background:

• The genetic code's evolution from ambiguity to precision is a key question in molecular evolution.
• Transfer RNA (tRNA) anticodon loop and stem structures are crucial for decoding mRNA codons.

Purpose of the Study:

• To propose a plausible evolutionary scenario for the genetic code's refinement.
• To explain the transition from an ambiguous triplet code to the present decoding system.

Main Methods:

• Analysis of general features of tRNA anticodon loops and stems.
• Consideration of present-day translation properties.
• Development of a model based on codon reading mechanisms.

Main Results:

• Primordial tRNA anticodons may have adopted 3' or 5' stacked conformations for "best two out of three" base pairing.
• Progressive structural constraints and base modifications led to a less ambiguous "two out of three" reading mechanism.
• Further adjustments resulted in the present generalized genetic code, expanding from 4-8 to 20 amino acids.

Conclusions:

• The evolution of the genetic code was a smooth process driven by structural and chemical modifications of tRNA.
• The proposed model explains the transition from an ambiguous to a precise decoding system.