Heterogeneity of nucleolar U3 ribonucleic acid of the Novikoff hepatoma.

Among the low molecular weight RNAs which have been shown to be localized to the nucleolus are the 4 S, U3, and 8 S RNAs. Of these, the U3 and 8 S RNAs are hydrogen bonded to nucleolar 28 S RNA. The nucleolar U3 RNA migrates as an electrophoretically homogeneous band on 8% polyacylamide gels but was separated into four bands on 16% gels. Although these bands have similar nucleotide compositions, chemical analysis of the hydroxymethyl ethylene glycol derivatives of the 3’-terminal nucleosides produced by periodate oxidation and reduction with tritiated potassium borohydride has shown that these bands contain several components. Separation on DEAR-Sephadex of the oligonucleotides obtained by TI and pancreatic RNase digestion showed that three difIerent groups of terminal oligonucleotides are present. The nucleoside peak contains 3’-terminal guanosine, SS%, and @dine, 15 %. The mononucleotide peak contains terminal adenosine, 62%, uridine, 26%, and @dine, 8%. The hexanucleotide peak contains terminal uridine, 100%. On the basis of the enzymatic digestions employed, the terminal oligonucleotides are PyG, PyC, PyGAA, PyGAU, PyGAC, PyG(N~)~NrnpNrnpU.