A novel lysine-substituted nucleoside in the first position of the anticodon of minor isoleucine tRNA from Escherichia coli

A minor species of isoleucine tRNA (tRNA(minor)(Ile)) specific to the codon AUA has been isolated from Escherichia coli B and a modified nucleoside N⁺ has been found in the first position of the anticodon (Harada, F., and Nishimura, S. (1974) Biochemistry 13, 300-307). In the present study, tRNA(minor)(Ile) was purified from E. coli A19, and nucleoside N⁺ was prepared, by high-performance liquid chromatography, in an amount (0.6 A₂₆₀ units) sufficient for the determination of chemical structures. By 400 MHz ¹H NMR analysis, nucleoside N⁺ was found to have a pyrimidine moiety and a lysine moiety, the ε-amino group of which was involved in the linkage between these two moieties. From the NMR analysis together with mass spectrometry, the structure of nucleoside N⁺ was determined as 4-amino-2-(N⁶-lysino)-1-(β-D-ribofuranoysl)pyrimidinium ('lysidine'), which was confirmed by chemical synthesis. Lysidine is a novel type of modified cytidine with a lysine moiety and has one positive charge. Probably because of such a unique structure, lysidine in the first position of anticodon recognizes adenosine but not guanosine in the third position of codon.