N-(3-amino-3-carboxypropyl)-β-carboxypyridinium betaine: A new amino acid from tobacco leaves

The RNA of an established line of Chinese hamster cells growing in cell culture contains a small number of uridines substituted at the 3-position with a γ-linked α-aminobutyrate residue. Structure has been ascertained by: (a) examination of incorporation of isotopic labels from precursors; (b) degradation with anhydrous hydrazine and comparison of the products with synthetic material or with hydrazinolysis products of known uridines; and (c) comparison of the unknowns as their hydantoin derivatives with the 5-β-(bromoethyl)hydantoin alkylation products of uridine and of 1- and 3-methylpseudouridine. In this manner it is shown that 18-S RNA of ribosomes contains a single residue of a nucleoside which we tentatively identify as 1-methyl-3-γ-(α-amino-α-carboxypropyl)pseudouridine per molecule. RNA isolated from the supernatant fraction, sedimenting at 4 S and co-electrophoresing with transfer RNA on polyacrylamide gels, contains several similar bases, one of which is identified as 3-γ-(α-amino-α-carboxypropyl)uridine. Each of the above nucleosides derives its α-aminobutyrate residue from methionine.