title: Amino acid modifications on tRNA.
abstract: The accurate formation of cognate aminoacyl-transfer RNAs (aa-tRNAs) is essential for the fidelity of translation. Most amino acids are esterified onto their cognate tRNA isoacceptors directly by aa-tRNA synthetases. However, in the case of four amino acids (Gln, Asn, Cys and Sec), aminoacyl-tRNAs are made through indirect pathways in many organisms across all three domains of life. The process begins with the charging of noncognate amino acids to tRNAs by a specialized synthetase in the case of Cys-tRNA(Cys) formation or by synthetases with relaxed specificity, such as the non-discriminating glutamyl-tRNA, non-discriminating aspartyl-tRNA and seryl-tRNA synthetases. The resulting misacylated tRNAs are then converted to cognate pairs through transformation of the amino acids on the tRNA, which is catalyzed by a group of tRNA-dependent modifying enzymes, such as tRNA-dependent amidotransferases, Sep-tRNA:Cys-tRNA synthase, O-phosphoseryl-tRNA kinase and Sep-tRNA:Sec-tRNA synthase. The majority of these indirect pathways are widely spread in all domains of life and thought to be part of the evolutionary process.
authors.affiliation: Department of Molecular Biophysics and Biochemistry, Yale University, New Haven, CT 06520-8114, USA.
authors.forename: Jing
authors.initials: J
authors.lastname: Yuan
authors.forename: Kelly
authors.initials: K
authors.lastname: Sheppard
authors.forename: Dieter
authors.initials: D
authors.lastname: Söll
mesh_terms: D000596:Amino Acids / Q000737:chemistry* / Q000235:genetics*; D008956:Models, Chemical; D008957:Models, Genetic; D046188:Protein Modification, Translational / Q000235:genetics*; D012343:RNA, Transfer / Q000737:chemistry* / Q000235:genetics*
chemical_list: D000596:Amino Acids; D012343:RNA, Transfer