title: Aminoacyl-tRNA synthesis by pre-translational amino acid modification.
abstract: Aminoacyl-tRNAs (aa-tRNAs) are essential substrates for ribosomal translation, and are generally synthesized by aminoacyl-tRNA synthetases (aaRSs). It was expected earlier that every organism would contain a complete set of twenty aaRSs, one for each canonical amino acid. However, analysis of the many known genome sequences and biochemical studies revealed that most organisms lack asparaginyl- and glutaminyl-tRNA synthetases, and thus are unable to attach asparagine and glutamine directly onto their corresponding tRNA. Instead, a pretranslational amino acid modification is required to convert Asp-tRNA(Asn) and Glu-tRNA(Gln) to the correctly charged Asn-tRNA(Asn) and Gln-tRNA(Gln), respectively. This transamidation pathway of amide aa-tRNA synthesis is common in most bacteria and archaea. Unexpected results from biochemical, genetic and genomic studies showed that a large variety of different bacteria rely on tRNA-dependent transamidation for the formation of the amino acid asparagine. Pretranslational modifications are not restricted to asparagine and glutamine but are also found in the biosynthesis of some other aa-tRNAs, such as the initiator tRNA fmet-tRNA(Met)(i) and Sec-tRNA(Sec) specifying selenocysteine, the 21(st) cotranslationally inserted amino acid. tRNA-dependent amino acid modification is also involved in the generation of aminolevulinic acid, the first precursor for porphyrin biosynthesis in many organisms.
authors.affiliation: Department of Molecular Biophysics, Yale University, New Haven, Connecticut 06520-8114, USA.
authors.forename: Liang
authors.initials: L
authors.lastname: Feng
authors.forename: Kelly
authors.initials: K
authors.lastname: Sheppard
authors.forename: Suk
authors.initials: S
authors.lastname: Namgoong
authors.forename: Alexandre
authors.initials: A
authors.lastname: Ambrogelly
authors.forename: Carla
authors.initials: C
authors.lastname: Polycarpo
authors.forename: Lennart
authors.initials: L
authors.lastname: Randau
authors.forename: Debra
authors.initials: D
authors.lastname: Tumbula-Hansen
authors.forename: Dieter
authors.initials: D
authors.lastname: Söll
mesh_terms: D000596:Amino Acids / Q000737:chemistry; D000604:Amino Acyl-tRNA Synthetases / Q000737:chemistry / Q000502:physiology*; D001105:Archaea / Q000378:metabolism; D001216:Asparagine / Q000737:chemistry; D001412:Bacillus subtilis / Q000378:metabolism; D002734:Chlorophyll / Q000737:chemistry; D004926:Escherichia coli / Q000378:metabolism; D005973:Glutamine / Q000737:chemistry; D006418:Heme / Q000737:chemistry; D008954:Models, Biological; D010802:Phylogeny; D011166:Porphyrins / Q000737:chemistry; D046188:Protein Modification, Translational; D012346:RNA, Transfer, Amino Acyl; D013045:Species Specificity
chemical_list: D000596:Amino Acids; D011166:Porphyrins; D012346:RNA, Transfer, Amino Acyl; D005973:Glutamine; D002734:Chlorophyll; D006418:Heme; D001216:Asparagine; D000604:Amino Acyl-tRNA Synthetases