Structural studies on isoleucyl‐tRNA synthetase from E. coli

IntroductionAminoacyl-tRNA synthetases play an important role in the translation of the genetic message.Very little is known about the protein chemistry of these enzymes and studies so far have been limited to the quaternary structures [1 ].The only sequence data are published by Bruton and Hartley [2] and cover special peptides of the methionyl-tRNA synthetase from E. coli.I report here sequence studies around the cysteine residues in isoleucyl-tRNA synthetase and the effect of these results on the structure of the enzyme. Materials ChemicalsJodo-[2-3H] acetic acid with a specific activity of 113 mCi/mM was purchased from the Radiochemical Centre (Amersham, England) and diluted with unlabeled iodoacetic acid just prior to use to give a specific activity of 10 mCi/mM.Phenylisothiocyanate was obtained from Fluka (Buchs, Swiss), redistilled and kept under nitrogen.Pyridine and trifluoroacetic acid were products from Merck (Darmstadt, Germany) and redistilled under nitrogen when used for sequence studies.Aquasol and omnifluor were obtained from NEN Chemicals (Dreieichenhain, Germany) and used for counting liquid samples or radioactivity on papers respectively.Micro-polyamide layers F 1700 and chromatography paper grade 2316 from Schleicher und Schi~ll (Dassel, Germany) were used for chromatography.Solvents and other chemicals used were purchased from Merck (Darmstadt, Germany) reagent grade or the highest purity available.