Nucleosome-associated proteins and phosphoproteins of differentiating Friend erythroleukemia cells.

Mononucleosomes derived from brief digestion of uninduced Friend cell nuclei with micrococcal nuclease contain a set of non-histone chromosomal proteins which are partly or altogether missing in the oligomeric nucleosomes. On the other hand, the latter contain a protein of Mr 190,000 not seen in the mononucleosomes. Longer digestion removes most of these non-histone proteins, excepting the Mr 190,000 protein. Brief digestion of nuclei from Friend cells induced by DMSO or by n-butyrate removes most of the non-histone proteins from the nucleosomes, as did the prolonged digestion of uninduced nuclei. The Mr 190,000 protein remains, while a protein of Mr 27,000 is increased. The rate of phosphorylation of histone H1 associated with mononucleosomes was 3 to 4-fold greater in cells induced with DMSO. The major phosphoprotein and most of the other phosphorylated non-histones were modified at the same rate in control and induced cells. However, a Mr 95,000 protein was less phosphorylated in the induced cells.