Structural Analysis of Nucleolar Precursors of Ribosomal Ribonucleic Acids: I. ISOLATION AND CHARACTERIZATION OF THE LONGEST POLYPURINE SEQUENCES OF NUCLEOLAR 28 S RIBONUCLEIC ACID AND RIBOSOMAL 28 S RIBONUCLEIC ACID OF NOVIKOFF HEPATOMA ASCITES CELLS

Abstract

Abstract For comparison of the oligonucleotides of highly labeled nucleolar and ribosomal 28 S RNA, the products of complete digestion with pancreatic RNase were separated by chromatography on DEAE-Sephadex A-25 at pH 7.6. The peaks containing several nonanucleotides, decanucleotides, one undecanucleotide, and one tetradecanucleotide were well defined. To separate the individual oligonucleotides, they were rechromatographed on DEAE-Sephadex A-25 at pH 3.3. Sequence studies were carried out by complete digestions with T1 RNase and with alkali and partial digestion with spleen phosphodiesterase. Complete sequences were defined for the nonanucleotides A-A-A-A-G-G-A-A-Cp, A-G-A-G-G-A-A-A-Cp, and G-G-G-A-A-G-A-G-Up. Partial sequences were determined for the nonanucleotides (Gp)(Gp)-(A-Gp)(A-Gp)-A-A-Cp and (A-A-A-A-Gp)(A-Gp)(Gp)Up, the decanucleotides (A-Gp)(Gp)(Gp)(Gp)-A-A-G-G-Up and (A-A-A-Gp)(A-Gp)(Gp)(Gp)(Gp)Up, the undecanucleotide (A-A-Gp)(A-Gp)(C-Gp)(Gp)(Gp)(Gp)Up, and the tetradecanucleotide (A-A-A-A-Gp)(A-Gp)(Gp)(Gp)(Gp)-A-A-A-Cp. In agreement with the hybridization and analytical studies reported earlier, each of the polypurine sequences found in nucleolar 28 S RNA was also isolated from ribosomal 28 S RNA, thereby providing more definitive chemical evidence that the nucleolar 28 S RNA is the precursor of 28 S ribosomal RNA.