title: Cysteinyl-tRNA synthetase is a direct descendant of the first aminoacyl-tRNA synthetase.
abstract: The gene encoding the cysteinyl-tRNA synthetase of E. coli was cloned from an E. coli genomic library made in lambda 2761, a lambda vector which can integrate and which carries a chloramphenicol resistance gene. A thermosensitive cysS mutant of E. coli was lysogenised and chloramphenicol-resistant colonies able to grow at 42 degrees C were selected to isolate phages containing the wild-type cysS gene. The sequence of the gene was determined. It codes for a 461 amino-acid protein and includes the sequences HIGH and KMSK known to be involved in the ATP and tRNA binding respectively of class I synthetases. The cysteinyl enzyme has segments in common with the cytoplasmic leucyl-tRNA synthetase of Neurospora crassa, the tryptophanyl-tRNA synthetase of Bacillus stearothermophilus, and the phenylalanyl-tRNA synthetase of Saccharomyces cerevisiae. Sequence comparisons show that the amino end of the cysteinyl-tRNA synthetase has similarities with prokaryotic elongation factors Tu; this region is close to the equivalent acceptor binding domain of the glutaminyl-tRNA synthetase of E. coli. There is a further similarity with the seryl enzyme (a class II enzyme) which has led us to propose that both classes had a common origin and that this was the ancestor of the cysteinyl-tRNA synthetase.
authors.affiliation: MRC Molecular Genetics Unit, Cambridge, UK.
authors.forename: J
authors.initials: J
authors.lastname: Avalos
authors.forename: L M
authors.initials: LM
authors.lastname: Corrochano
authors.forename: S
authors.initials: S
authors.lastname: Brenner
mesh_terms: D000595:Amino Acid Sequence; D000604:Amino Acyl-tRNA Synthetases / Q000737:chemistry* / Q000235:genetics*; D001483:Base Sequence; D003001:Cloning, Molecular; D004269:DNA, Bacterial; D004926:Escherichia coli / Q000201:enzymology / Q000235:genetics; D015723:Gene Library; D008969:Molecular Sequence Data; D010444:Peptide Elongation Factor Tu / Q000737:chemistry; D016415:Sequence Alignment; D013696:Temperature
chemical_list: D004269:DNA, Bacterial; D010444:Peptide Elongation Factor Tu; D000604:Amino Acyl-tRNA Synthetases; C019975:cysteinyl-tRNA synthetase