Collegium Budapest, Hungary, and The Parmenides Foundation for the Study of Thinking, Munich, Germany
A theoretical biologist recommends thought-provoking reading on the origin of translation and the genetic code.
As Francis Crick and his co-workers once noted, “the origin of protein synthesis is a notoriously difficult problem”. Our best hopes of resolving this problem begin, in my opinion, in an RNA world.
The RNA-world hypothesis holds that RNA emerged before DNA and proteins, neatly separating the origin of life from that of the genetic code and its translation. The question then becomes: how did RNA evolve to make proteins?
In a recent paper, Yuri Wolf and Eugene Koonin of the National Institutes of Health in Bethesda, Maryland, present one scenario (Biol. Direct 2, 14; 2007).
They rightly call attention to studies that suggest that protein-based aminoacyl-tRNA synthetases, which are involved in the first steps of assembling amino acids into proteins, are relatively late evolutionary inventions. This forces us to accept the idea that protein synthesis is older than such synthetases.
Before the evolution of synthetases, the only agents that could conceivably have marshalled amino acids are RNA enzymes, or ribozymes. Wolf and Koonin share my view that the recruitment of amino acids was driven by selection for enhanced catalytic activity, and that the ancestor of the large ribosomal RNA that catalyses protein synthesis in today’s cells — a molecular ‘fossil’ — was a catalyst that linked only two amino acids.
I am less happy with these authors’ suggestion of a relatively late switch from peptide-specific proto-ribosomes to those that could use an external template such as mRNA to synthesize peptides with arbitrary sequence — but they may well be right.
They lay out an evolutionary sequence that is more complete than the scenario I once proposed. I highly recommend this well-written, thought-provoking paper.