Phosphorylation in vivo and in vitro of Proteins from HeLa Cells: Heterogeneous Nuclear Ribonucleoprotein Particles

Abstract

We have used high-resolution two-dimensional gel electrophoresis (O'Farrell, 1975) to study the proteins of hnRNA*-protein particles from CVl monkey cells. hnRNAprotein was isolated by sonication of nuclei and further purified asdescribed by Peterson (1974). Chromatin, hnRNA-protein and nucleosol fractions of the nuclear extract were analysed for their protein constituents. As shown by two-dimensional gel electrophoresis, hnRNA is associated with a distinct class of about 30 proteins different from the proteins of chromatin and nucleosol fractions. Some polymeric proteins, such as * Abbreviation: hnRNA, heterogeneous nuclear RNA.

Peptide mapping of in vivo and in vitro phosphorylated sites of proteins from HeLa hnRNP

“…wt 28 000 and 37 000 M r [7]. These same species, along with 2 other ones of 30 000 and 52 000 M r, are also phosphorylated in vivo after exposure of cells to [32P]orthophosphate [9,10]. Further evidence towards showing that purified hnRNP have retained the native character and specific phosphorylation properties which they exhibited in vivo should come from the demonstration that the same amino acid sites are involved in both…”