Wheat-Embryo Ribonucleates. III. Modified Nucleotide Constituents in Each of the 5.8S, 18S and 26S Ribonucleates

Abstract

Modified nucleotide constituents in the NaCl-insoluble (2.5 M, 0 °C) fraction of wheat-embryo RNA (iRNA) have been efficiently labelled by imbibing wheat embryos in media that contain [³²P]phosphate and/or [methyl-¹⁴C]methionine. Chromatographic analyses have shown that pseudouridylate and sugar-methylated nucleotides (each) account for a similar proportion (1–2 mol %) of the total nucleotides in alkali hydrolysates of each of the 5.8S, 18S and 26S components of wheat-embryo iRNA. All of the 16 possible sugar-methylated dinucleotide sequences (Nm-N) that can be formed by permuting the arrangement of the four classical ribonucleosides (N) and their O²′-methylated derivatives (Nm) are present in the 18S component, and all except Cm-G are present in the 26S component of wheat-embryo iRNA. Two sugar-methylated dinucleotide sequences (Am-A and Gm-C) are present in the 5.8S component. All of the (approximately seven) sugar-methylated trinucleotide sequences (Nm-Nm-N) are confined to the 26S component. The base-methylated nucleotide N⁶-monomethyladenylate is present in both 18S and 26S components, but the base-methylated nucleotide N⁶-dimethyladenylate is confined to the 18S component. An allied investigation of the NaCl-soluble (2.5 M, 0 °C) fraction of wheat-embryo RNA (sRNA) has shown that an alkali hydrolysate of the 5S component of the s[³²P]RNA is virtually devoid of modified compounds.