On origin of genetic code and tRNA before translation

Area of Science:

• Origin of Life
• Molecular Evolution
• Genetics

Background:

• The genetic code, assigning codons to amino acids, presents a
• key-lock vs. frozen accident
• dilemma regarding its origin.
• Re-examining this dilemma involves considering the absence of foresight evolution, modular tRNA and aminoacyl-tRNA synthetase structures, and in vitro selected RNA aptamers.

Purpose of the Study:

• To investigate the origins of the genetic code assignment.
• To explore the role of RNA aptamers and tRNA structures in the code's emergence.
• To propose a model for tRNA origin and the co-evolution of translation machinery.

Main Methods:

• Analysis of RNA aptamer binding sites for eight amino acids, focusing on codon and anticodon interactions.
• Examination of palindrome-dinucleotide associations within codons and anticodons.
• In vitro selection of amino acid-specific RNA aptamers.

Main Results:

• RNA binding sites for arginine, isoleucine, and tyrosine contain both cognate codons and anticodons, often associated with palindrome-dinucleotides.
• A significant preference was observed for anticodon(2-3)/codon(1-2) tetramers over anticodon(1-2)/codon(2-3) counterparts, supporting a pre-translational code origin.
• A model for tRNA origin is proposed, involving gradual elongation from primordial coding elements.

Conclusions:

• Primordial tRNAs and translation machinery likely co-evolved to fit a pre-defined genetic code.
• The second and third nucleotides of coding triplets were initially more important than the first.
• The evolutionary primacy of anticodons suggests a harmonious coexistence of various hypotheses regarding the code's origin.