Base composition of terminal polynucleotides isolated from mouse ascite nucleolar RNA

Two species of high molecular weight RNA were isolated from the nucleoli of mouse ascite tumor cells. The 3′-terminal nucleotide fragments of these high molecular weight RNA species were obtained after digestion of the RNA with RNase T₁, oxidation of the terminus with sodium periodate and isolation on aminoethyl cellulose. The terminal fragments behaved differently upon chromatography on DEAE-cellulose. These fragments contained different base compositions as follows: fragment A - Ap 24.7%, Cp 50.3%, and Up 25.0%; fragment B - Ap 40.7%, Cp 16.8%, and Up 43.5%. The terminal polynucleotide sequences of the 41S and 45S RNAs are -Gp(Ap, Up, 2Cp)X_OH and -Gp(2Ap, 2Up, Cp)X_OH respectively where X is unknown at the present. These data are discussed in regard to the various models proposed for the organization of nucleotide sequences of rRNA within the nucleolar precursors.