Structural Analysis of Nucleolar Precursors of Ribosomal Ribonucleic Acids: SEQUENCE ANALYSIS OF LONG OLIGONUCLEOTIDES PRODUCED BY T1 RIBONUCLEASE DIGESTION OF NUCLEOLAR AND RIBOSOMAL 28 S RIBONUCLEIC ACID OF NOVIKOFF HEPATOMA ASCITES CELLS

Abstract

Abstract Complete T1 RNase digestion was carried out on nucleolar precursor and ribosomal 28 S RNA of Novikoff ascites tumor cells which were highly labeled in vitro with [32P]orthophosphate. Two large fragments, having chain lengths of 28 and 20 nucleotides, were isolated in highly purified form from digests of both nucleolar precursor and ribosomal 28 S RNA by successive chromatography on DEAE-Sephadex at pH 7.5 and DEAE-Sephadex at pH 3.3. One of the fragments, referred to as the δ fragment, has a chain length of 28 nucleotides and is the largest fragment produced by T1 RNase from the 28 S RNA. The other fragments, referred to as the β fragment, contains an alkali-stable dinucleotide Cm-Up. Sequence studies were carried out on these fragments with the aid of complete and partial pancreatic RNase digestion, U2 RNase digestion, and partial spleen phosphodiesterase digestion. The sequences of A-A-C-C-U-A-U-C-U-U-C-A-U-C-U-C-A-A-A-C-U-U-U-A-A-A-U-G for the δ fragment and A-A-A-U-A-C-C-A-Cm-U-A-C-U-U-C-C-A-U-C-G for the β fragment are the longest obtained thus far for either ribosomal 28 S RNA or nucleolar 28 S RNA. The sequences of these two large fragments were identical for nucleolar and ribosomal 28 S RNA and provide further chemical evidence for the nucleolar origin of ribosomal 28 S RNA.