title: Evidence for the early divergence of tryptophanyl- and tyrosyl-tRNA synthetases.
abstract: Each amino acid is attached to its cognate tRNA by a distinct aminoacyl-tRNA synthetase (aaRS). The conventional evolutionary view is that the modern complement of synthetases existed prior to the divergence of eubacteria and eukaryotes. Thus comparisons of prokaryotic and eukaryotic aminoacyl-tRNA synthetases of the same type (charging specificity) should show greater sequence similarities than comparisons between synthetases of different types-and this is almost always so. However, a recent study [Ribas de Pouplana L, Furgier M, Quinn CL, Schimmel P (1996) Proc Natl Acad Sci USA 93:166-170] suggested that tryptophanyl- (TrpRS) and tyrosyl-tRNA (TyrRS) synthetases of the Eucarya (eukaryotes) are more similar to each other than either is to counterparts in the Bacteria (eubacteria). Here, we reexamine the evolutionary relationships of TyrRS and TrpRS using a broader range of taxa, including new sequence data from the Archaea (archaebacteria) as well as species of Eucarya and Bacteria. Our results differ from those of Ribas de Pouplana et al.: All phylogenetic methods support the separate monophyly of TrpRS and TyrRS. We attribute this result to the inclusion of the archaeal data which might serve to reduce long branch effects possibly associated with eukaryotic TrpRS and TyrRS sequences. Furthermore, reciprocally rooted phylogenies of TrpRS and TyrRS sequences confirm the closer evolutionary relationship of Archaea to eukaryotes by placing the root of the universal tree in the Bacteria.
authors.affiliation: Department of Biochemistry, Canadian Institute for Advanced Research, Dalhousie University, Sir Charles Tupper Building, Halifax, Nova Scotia, Canada. James_R_Brown@sbphrd.com
authors.forename: J R
authors.initials: JR
authors.lastname: Brown
authors.forename: F T
authors.initials: FT
authors.lastname: Robb
authors.forename: R
authors.initials: R
authors.lastname: Weiss
authors.forename: W F
authors.initials: WF
authors.lastname: Doolittle
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001105:Archaea / Q000235:genetics; D005075:Biological Evolution; D004269:DNA, Bacterial / Q000235:genetics; D006801:Humans; D008969:Molecular Sequence Data; D010802:Phylogeny; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid; D014369:Tryptophan-tRNA Ligase / Q000235:genetics*; D014448:Tyrosine-tRNA Ligase / Q000235:genetics*
chemical_list: D004269:DNA, Bacterial; D014448:Tyrosine-tRNA Ligase; D014369:Tryptophan-tRNA Ligase