Characterization of Pre‐messenger‐RNA‐Containing Nuclear Ribonucleoprotein Particles from Avian Erythroblasts

Abstract

Ribonucleoprotein [RNP] particles were isolated from duck erythroblast nuclei using a procedure designed to produce maximal cytoplasmic dispersion with minimal release of endogenous hydrolytic enzymes. The RNA extracted from the purified nuclear RNP fraction contains globin mRNA sequences at a concentration comparable to that present in total nuclear RNA. The polypeptide composition of this fraction revealed by electrophoresis in 2 dimensions is complex, consisting of at least 65 acidic species and 21 basic species. Several lines of evidence suggest that these are authentic components of nuclear RNP. The so-called core proteins of nuclear RNP which were previously shown to migrate as a single band on low-pH urea gels and as 6 bands on sodium dodecyl sulfate gels were considerably more complex, being resolved by 2-dimensional electrophoresis into a group of 15 basic and 6 more and less neutral polypeptides. Isoelectric focusing of nuclear RNP under non-denaturing conditions suggests that these latter species are not uniformly distributed along the pre-mRNA molecule.