Properties of a nuclear polyadenylate-protein complex from mouse ascites cells

Ribonucleoprotein (RNP) subcomplexes containing at least 60% of the total nuclear poly(A) were isolated from mouse ascites cells; these 15 S ribonucleoprotein particles were most probably derived from larger hnRNA containing complexes. The buoyant density of the 15 S ribonucleoprotein in formaldehyde-CsCl was significantly less than that of the hnRNA-containing 30 S ribonucleoprotein subcomplex, indicating a higher proportion of protein (approximately 80%) in the 15 S ribonucleoprotein. The proteins partially protected the poly(A) from the action of ribonuclease T2. RNA isolated from purified 15 S ribonucleoprotein was estimated to be 190 to 200 nucleotides in length by gel electrophoresis, whereas the RNA from crude preparations was slightly larger. Base composition analysis of 32P-labeled crude 15 S RNP-RNA showed it to be rich in adenylate (70%) but containing a substantial amount of uridylate (20%). The base composition of RNA from purified complexes was approximately 90% adenyalte. Our results suggested that oligo(U) sequences from hnRNA could artificially associated with the poly(A) during preparation of 15 S RNP-RNA.