MODIFICATION OF NUCLEOSIDES AND NUCLEOTIDES .8. REACTION RATES OF PSEUDOURIDINE RESIDUES WITH ACRYLONITRILE AND ITS RELATION TO SECONDARY STRUCTURE OF TRANSFER RIBONUCLEIC ACID

1. Approx. one-third of the total pseudouridine (ψ) residues in yeast transfer RNA (tRNA) were rapidly cyanoethylated by acrylonitrile at pH 8.6 and 40-42° in 2.7 M aqueous dimethylformamide solution when the medium contained 0.5 M NaCl. On the other hand, the rate of the cyanoethylation of the ψ residues markedly decreased when the NaCl was replaced with 2 mM MgCl2. 2. The results of several experiments designed to clarify this phenomena indicated that the effect of salts on the rate of the cyanoethylation is probably caused by stabilization of the secondary or tertiary structure of tRNA. 3. The ψ residue contained in the common tetranucleotide sequence, TpψpCpGp, of tRNA was not involved in the one-third of the total ψ residues which were rapidly cyanoethylated in the presence of 0.5 M NaCl. The results suggested that this common sequence is probably buried in a rather stable part of the secondary or tertiary structure of tRNA. 4. Most ψ residues in tRNA seemed to be buried in the conformational structure of tRNA when the structure was stabilized in a medium containing Mg2+. © 1968.