Widespread use of the glu-tRNAGln transamidation pathway among bacteria. A member of the alpha purple bacteria lacks glutaminyl-trna synthetase.
The expression of the Rhizobium meliloti glutamyl-tRNA synthetase gene in Escherichia coli under the control of a trc promoter results in a toxic effect upon isopropyl-beta-D-thiogalactopyranoside induction, which is probably caused by a misacylation activity. To further investigate this unexpected result, we looked at the pathway of Gln-tRNAGln formation in R. meliloti. No glutaminyl-tRNA synthetase activity has been found in R. meliloti crude extract, but we detected a specific aminotransferase activity that changes Glu-tRNAGln to Gln-tRNAGln. Our results show that R. meliloti, a member of the alpha-subdivision of the purple bacteria, is the first Gram-negative bacteria reported to use a transamidation pathway for Gln-tRNAGln synthesis. A phylogenetic analysis of the contemporary glutamyl-tRNA synthetase and glutaminyl-tRNA synthetase amino acid sequences reveals that a close evolutionary relationship exists between R. meliloti and yeast mitochondrial glutamyl-tRNA synthetases, which is consistent with an origin of mitochondria in the alpha-subdivision of Gram-negative purple bacteria. A 256-amino acid open reading frame closely related to bacterial glutamyl-tRNA synthetases, which probably originates from a glutamyl-tRNA synthetase gene duplication, was found in the 4-min region of the E. coli chromosome. We suggest that this open reading frame is a relic of an ancient transamidation pathway that occurred in an E. coli ancestor before the horizontal transfer of a eukaryotic glutaminyl-tRNA synthetase (Lamour, V., Quevillon, S., Diriong, S., N'Guyen, V. C., Lipinski, M., and Mirande, M.(1994) Proc. Natl. Acad. Sci. U. S. A. 91, 8670-8674) and that it favored its stable acquisition. From these observations, a revisited model for the evolution of the contemporary glutamyl-tRNA synthetases and glutaminyl-tRNA synthetases that differs from the generally accepted model for the evolution of aminoacyl-tRNA synthetases is proposed.
Gagnon
Y
Y
Département de Biochimie, Faculté des Sciences et de Génie, Université Laval, Ste-Foy, Québec G1K 7P4, Canada.
Lacoste
L
L
Champagne
N
N
Lapointe
J
J
D000595:Amino Acid Sequence; D000604:Amino Acyl-tRNA Synthetases / Q000096:biosynthesis / Q000737:chemistry* / Q000378:metabolism*; D002851:Chromatography, High Pressure Liquid; D003001:Cloning, Molecular; D016001:Confidence Intervals; D004790:Enzyme Induction; D004926:Escherichia coli / Q000378:metabolism*; D005798:Genes, Bacterial; D005975:Glutamate-tRNA Ligase / Q000737:chemistry*; D007544:Isopropyl Thiogalactoside / Q000494:pharmacology; D008969:Molecular Sequence Data; D010802:Phylogeny; D011401:Promoter Regions, Genetic; D012346:RNA, Transfer, Amino Acyl / Q000302:isolation & purification / Q000378:metabolism*; D012351:RNA, Transfer, Gln / Q000378:metabolism*; D011994:Recombinant Proteins / Q000096:biosynthesis / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D016962:Sinorhizobium meliloti / Q000201:enzymology* / Q000235:genetics; D014166:Transferases / Q000378:metabolism*
D012346:RNA, Transfer, Amino Acyl; D012351:RNA, Transfer, Gln; D011994:Recombinant Proteins; D007544:Isopropyl Thiogalactoside; D014166:Transferases; D000604:Amino Acyl-tRNA Synthetases; D005975:Glutamate-tRNA Ligase; C020659:glutaminyl-tRNA synthetase