SELECTIVE INACTIVATION OF E COLI TRNA BY ETHYLENIMINE

Studies in this laboratory on the S-aminoethylation of cysteine by ethylenimine while attached to transfer RNA (tRNA) led to the observation that the ability of E. coli B tRNA to accept certain amino acids was abolished by exposure to this reagent. The demonstration of limiting amounts of thiopyrimidines, predominantly 4-thiouridine, in E. coli tRNA by Lipsett (1965) led us to consider the S-aminoethylation of thionucleotides as a possible explanation for the selective inactivation of amino acid acceptance by ethylenimine. The present communication demonstrates that aminoethylation by ethylenimine of 4-thiouridine residues in E. coli tRNA does occur under conditions mild enough to avoid covalent rupture of tRNA molecules. The kinetics of alkylation of 4-thioU residues as well as the kinetics of inactivation of acceptance for four different amino acids are reported. © 1968.