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MBE Advance Access published online on December 20, 2006
Molecular Biology and Evolution, doi:10.1093/molbev/msl202
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© 2006 The Authors
This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/2.0/uk/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

Research Article

Origin and Evolution of the Mitochondrial Aminoacyl-tRNA Synthetases

Björn Brindefalk, Johan Viklund, Daniel Larsson, Mikael Thollesson and Siv G.E. Andersson

Department of Molecular Evolution, Evolutionary Biology Center, Uppsala University, 752 36 Uppsala, Sweden

Corresponding author: Siv G. E. Andersson, Department of Molecular Evolution, Norbyvägen 18C, S-752 36 Uppsala, Sweden, Tel: +46-18-4714379, FAX: +46-18-471 64 04, E-mail: Siv.Andersson{at}ebc.uu.se

Accepted for publication December 12, 2006.

Many theories favour a fusion of two prokaryotic genomes for the origin of the eukaryotes, but there are disagreements on the origin, timing and cellular structures of the cells involved. Equally controversial is the source of the nuclear genes for mitochondrial proteins, although the {alpha}-proteobacterial contribution to the mitochondrial genome is well established. Phylogenetic inferences show that the nuclearly encoded mitochondrial aaRSs occupy a position in the tree that is not close to any of the currently sequenced {alpha}-proteobacterial genomes, despite cohesive and remarkably well-resolved {alpha}-proteobacterial clades in 12 of the 20 trees. Two or more {alpha}-proteobacterial clusters were observed in 8 cases, indicative of differential loss of paralogous genes or horizontal gene transfer. Replacement and retargeting events within the nuclear genomes of the eukaryotes was indicated in 10 trees, 4 of which also show split {alpha}-proteobacterial groups. A majority of the mitochondrial aminoacyl-tRNA synthetases originate from within the bacterial domain, but none specifically from the {alpha}-proteobacteria. For some aminoacyl-tRNA synthetases, the endosymbiotic origin may have been erased by on-going gene replacements on the bacterial as well as the eukaryotic side. For others that accurately resolve the {alpha}-proteobacterial divergence patterns the lack of affiliation with mitochondria is more surprising. We hypothesize that the ancestral eukaryotic gene pool hosted primordial "bacterial-like" genes, to which a limited set of {alpha}-proteobacterial genes, mostly coding for components of the respiratory chain complexes, were added and selectively maintained.

Key Words: mitochondria • phylogeny • aminoacyl-tRNA synthetase


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