A Model for the Origin of the First mRNAs

Area of Science:

• Origin of Life
• Molecular Evolution
• Genetics

Background:

• The origin of the genetic code is a fundamental question in understanding the emergence of life.
• Early life likely relied on catalytic RNA molecules (ribozymes) before the advent of proteins.
• The transition from simple prebiotic chemistry to a coded system for protein synthesis remains poorly understood.

Purpose of the Study:

• To propose a novel model for the origin and evolution of the genetic code.
• To explain the emergence of the first messenger RNAs (mRNAs) and the transition to a triplet code.
• To identify a potential molecular fossil supporting the proposed evolutionary pathway.

Main Methods:

• Theoretical modeling of early RNA-RNA interactions and catalysis.
• Postulating selective pressures favoring improved catalytic efficiency and coding.
• Identifying existing molecules that fit the predicted characteristics of ancestral RNAs.

Main Results:

• A model where peptidated-RNAs acted as early catalysts, with pre-mRNAs evolving to direct these interactions.
• The initial genetic code likely involved larger base pairings (ennuplets) that evolved towards triplets for efficiency.
• The transfer-messenger RNA (tmRNA) molecule is proposed as a remnant of this early pre-mRNA stage.

Conclusions:

• The genetic code evolved from RNA-RNA interactions driven by the need for efficient catalyst synthesis.
• The transition to a triplet code was a natural selection for uniformity and efficiency.
• The tmRNA molecule provides strong evidence for this proposed evolutionary pathway of early mRNAs.