Isolation and characterization of nuclear particles containing rapidly labelled hnRNA and snRNA in combination with a distinct set of polypeptides of Mr 74 000 and 72 000

Abstract

A heterogeneous RNP structure has been isolated from rat liver nuclei by a method previously used for the isolation of 30S RNP complexes carrying heterogeneous RNA (hnRNA) [1]. The RNP sediments in sucrose gradients with s-values of 70–110S. Formaldehyde-fixed preparations band at ρ = 1.40 in isopycnic CsCl gradients. The RNP structure is composed of a heterogeneous population of polypeptides, prominent among which are two proteins with M r 74 000 and 72 000. It contains both rapidly labelled RNA as well as several species of snRNA, as demonstrated by double-labelling experiments and gel electrophonesis. Treatment of rats with α-amanitin leads to a significant decrease in the amount of recovered RNP. In the presence of 0.7 M NaCl the s-value of the complex changes from 70–110S to 40–80S. The RNP structure is stable to mild RNase A or micrococcal nuclease digestion. Transmission electron microscopy reveals the presence of a heterogeneous population of particles with a mean diameter of 300–360 Å. The isolated RNP structure differs completely from the well-known monoparticle or polyparticle hnRNP complexes and from the 30S or smaller snRNP particles but could be similar to or identical with the heterogeneous complex described by Jacob et al. [29].