Did Gene Expression Co-evolve with Gene Replication?

Abstract

We assemble recent experimental work on the aminoacyl-tRNA syn- thetase evolution into the context of theoretical studies on the nature of the problems preventing the emergence of genetic coding. What initially appeared as experimen- tal curiosities—evidence for ancestral bidirectional coding of the two synthetase classes, the extended inversion symmetries in higher-order structure and function- ality, and the strong correlations between amino acid physical chemistry and both protein folding and the tRNA identity elements used by synthetases to recognize cognate tRNAs—fit the landscape painted by the theoretical studies like a hand in a glove. We conclude that the prevailing RNA World scenario does not furnish an adequate basis for genetic coding. An important corollary is that the evolution of gene expression was very closely coupled to that of gene replication.