Journal of Molecular Evolution

, Volume 65, Issue 4, pp 425–436

Signature of a Primitive Genetic Code in Ancient Protein Lineages


DOI: 10.1007/s00239-007-9024-x

Cite this article as:
Fournier, G.P. & Gogarten, J.P. J Mol Evol (2007) 65: 425. doi:10.1007/s00239-007-9024-x


The genetic code is the syntactic foundation underlying the structure and function of every protein in the history of the biological world. Its highly ordered degenerate complexity suggests an incremental evolution, the result of a combination of selective, mechanistic, and random processes. These evolutionary processes are still poorly understood and remain an open question in the study of early life on Earth. We perform a compositional analysis of ribosomal proteins and ATPase subunits in bacterial and archaeal lineages, using conserved positions that came and remained under purifying selection before and up to the most recent common ancestor. An observable shift in amino acid usage at these conserved positions likely provides an untapped window into the history of protein sequence space, allowing events of genetic code expansion to be identified. We identify Cys, Glu, Phe, Ile, Lys, Val, Trp, and Tyr as recent additions to the genetic code, with Asn, Gln, Gly, and Leu among the more ancient. Our observations are consistent with a scenario in which genetic code expansion primarily favored amino acids that promoted an increase in polypeptide size and functionality. We propose that this expansion would have been critical in the takeover of many RNA-mediated processes, as well as the addition of novel biological functions inaccessible to an RNA-based physiology, such as crossing lipid membranes. Thus, expansion of the genetic code likely set the stage for the transition from RNA-based to protein-based life.


Evolution of the genetic code RNA world Most recent common ancestor Ribosome Ribosomal proteins ATPase Origin 

Supplementary material

239_2007_9024_MOESM1_ESM.pdf (322 kb)
ESM1 (PDF 321 kb)

Copyright information

© Springer Science+Business Media, LLC 2007

Authors and Affiliations

  1. 1.Department of Molecular and Cell BiologyUniversity of ConnecticutStorrsUSA

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