Modified Nucleosides of Nuclear and Nucleolar Low Molecular Weight Ribonucleic Acid

Abstract

Abstract Modified nucleosides have been found in some types of low molecular weight nuclear RNA of Novikoff hepatoma ascites cells in addition to 4 S RNA. The low molecular weight nuclear RNA species have been defined on the basis of their size as well as their content of uridylic acid as 4 S, 4.5 S, 5 S, U-1, U-2, and U-3 RNA (Busch, H., and Smetana, K. (1970) The Nucleolus, p. 285, Academic Press, New York). In particular, the U-2 RNA contained 11 pseudouridine residues and the unusual nucleoside, N2,N2-dimethyl 7-methyl guanosine, which was not found in transfer RNA or any other nuclear RNA except U-3. Nuclear 4.5 S RNAiii contained 3 pseudouridine residues and 1 residue each of N6-methyl adenosine and N2-methyl guanosine. Nuclear 5 S RNAiii contained 2 pseudouridine residues. Although the content of modified nucleosides in the 4 S RNAs from cytoplasm, ribosomes, and nuclei was the same, significantly lower amounts of dihydrouridine and N2-methyl guanosine were found in the nucleolar 4 S RNA. No modified nucleosides were found in 4.5 S RNAi, 4.5 S RNAii, 5 S RNAi, 5 S RNAii, U-1a RNA, and 5.5 S RNA.