Tae Suk Ro-Choi

Low-Molecular-Weight Nuclear RNAs

[1, p. 285; 2-14]. Some RNAs smaller in size than these which contain dihydrouridine or dihydrothymidine have also been reported to be present in the nucleus, specifically in association with the chromatin fraction [15-20]. Although the functions of most of these LMWN RNAs are not defined, their specificity of localization in the nucleolus and the nuclear chromatin fraction along with the number of these molecules (which approximates that of the number of functional genes) has suggested they may have an initiating or structural role in gene readouts or a regulatory role in gene function [8, 10, 2123]. The recent findings which have indicated that some low-molecular-weight nucleolar RNAs have specific temporal associations with newly synthesized ribosomal precursors suggest the possibility that they may be involved in specific phases of synthesis or modification of the ribosomal precursors [24]. Number of low-molecular-weight nuclear RNAs.—In a search for a definite role for these molecules in cell function, one of the critical problems has been the clarification of the number of types of these RNA molecules. Although it is not yet possible to specify with precision the total number of low-molecular-weight RNA species in the various fractions of the nucleus, the minimal estimate is eleven (fig. 1), and the maximum is approximately forty-three [1, 25]. None of these values, however, exclude possible microheterogeneity of the various nuclear RNA species. Table 1 indicates that there are at least

5S RNAIII, a new nucleus-specific 5S RNA

A new species of 5S RNA, referred to as 5S RNAIII, has been found in the Novikoff hepatoma ascites cell nuclei. This RNA, which composes 28% of total nuclear 5S RNA and co-migrates with ribosomal 5S RNAI and 5S RNAII on 8% polyacrylamide gel electrophoresis, has been isolated by chromatography on DEAE Sephadex columns. The nucleotide composition is A 24, U 31, G 24 and C 20; its A+UG+C ratio is 1.24. T1 RNase digestion produced the following unique oligonucleotides from 5S RNAIII: (U2C2)Gp, (CUA)Gp, (C4A3U8)Gp, [(UmU) (C2A3U5) (AGmC)], (CAU2)Gp, (C2AU2)Gp and (C3A3U2)Gp. Similarly, unique oligonucleotides were produced by complete pancreatic RNase digestion of 5S RNAIII, including UmUp, A-A-Up, A-A-Cp, (AG)Cp, A-Gm-Cp, (A2G)Up, A-A-A-Up and (A3G)-Up.

Two-dimensional polyacrylamide gel electrophoresis separation of low molecular weight nuclear RNA.

Summary Two-dimensional electrophoresis successively on 10%, pH 7.2, and 12%, pH 3.3, polyacrylamide gels was used to separate nuclear and whole cell 4–8S RNA fractions from Novikoff hepatoma ascites cells into individual RNA species. With this method, analytical studies were possible on two new species of RNA referred to as 4.2S RNA and 4.5S RNAII, respectively. The 4.2S RNA has the nucleotide composition AMP, 18.0; UMP, 23.9; GMP, 27.9; and CMP 26.7. This RNA contains 2 ψMP residues and an alkali stable dinucleotide. The 4.5S RNAII was distinctly separated from 4.5S RNAI and 4.5S RNAIII and has the nucleotide composition AMP, 20.6%; UMP, 23.7%; GMP, 30.0%; and CMP, 25.7%. It has no ψMP or 2′-0-methylated nucleotides. In addition, several other spots were separated from the major RNA species.

Low molecular weight nuclear RNA. The 3′-terminal sequence of the U2 RNA

SummaryThe U2 RNA is one of the low molecular weight nuclear RNAs of Novikoff hepatoma ascites cells that is specifically localized in the extranucleolar portion of the nucleus. After the RNA was purified by polyacrylamide gel electrophoresis, it was subjected to various enzymatic digestion procedures for determination of its primary sequence of nucleotides. The U2 RNA contains 197 nucleotides. Its 5′ end, which is highly modified, contains N2, 2, 7-trimethyl guanylic acid and 11 pseudouridylic acid residues (Reddy et al, J. Biol. Chem. 247, 7245–7250, 1972) in addition to 10 2′-O-methyl ribose residues.Its 3′-terminal portion (128 nucleotides) contains no methylated nucleotides and its sequence is:-A-U-A-C-G-U-C-C-U-C-U-A-U-C-C-G-A-G-G-A-C-A-A-U-A-ψ-U-A-ψ-U-A-A-A-U-G-G-A-U-U-U-U-U-G-G-A-A-C-U-A-G-G-A-G-U-U-G-G-A-A-U-A-G-G-A-G-C-U-U-G-C-U-C-C-G-U-C-C-A-C-C-U-C-A-C-G-C-A-U-C-G-A-C-C-U-G-G-U-A-U-U-G-C-G-C-A-G-U-A-C-C-C-U-C-A-G-G-A-A-C-G-G-U-G-C-A-C-C-AO H.