Pseudouridine, a Carbon-Carbon Linked Ribonucleoside in Ribonucleic Acids: Isolation, Structure, and Chemical Characteristics

Abstract

Until the invention of chromatographic analytical methods (l), which do not depend upon the precipitation of major components of complex mixtures, knowledge of the constituents of nucleic acids was confined to the principal bases, adenine, guanine, cytosine, uracil, and thymine, and their nucleosides and nucleotides. Although the existence of isomeric forms of the nucleotides was the first discovery attributable to the new methods (3, 4), the presence of 5-methylcytosine (5, 6) (and later 5-hydroxymethylcytosine (7)) in deoxyribonucleic acids constituted the 6rst indication of different bases. At about the same time, unidentified peaks (and spots) began to appear in chromatograms of RNA hydrolysates. Some of these were compounds of one or more of the known nucleotides (in polynucleotide form, for example), but others, more recently recognized, have been identified as methyl derivatives of the common RNA nucleotides occurring in small amounts (8, 9). All of the more recently discovered bases, as with 5-methylcytosine, occur in the usual N-ribosyl linkage. However, the first “minor” nucleotide from RNA to appear (Fig. 1 of Cohn and Volkin (lo), peak labeled ?) was not readily identified with such a linkage. In retrospect it seems likely that the difficulty derives from the fact, demonstrated in this paper, that the base-ribosyl linkage is not C-N but C-C. The isolation and certain of the physical and chemical properties of this unusual nucleoside have been described (la, ll13). Much of the chemical and physical evidence that establishes its structure as 5-ribosyluracil has been summarized previously (la) and the term pseudouridine has been proposed for a trivial name. In this paper are described certain of the chemical, chromatographic, spectrophotometric, and nuclear magnetic properties of the substance and its derivatives that pertain to the question of structure and natural occurrence.