Gene activation during muscle differentiation and the role of nonhistone chromosomal protein phosphorylation

Comparative studies of nuclear phosphoproteins from four different muscle tissues and liver

1. Nuclei isolated from red and white skeletal muscle, heart, uterus and liver of rabbit were incubated with [lambda-32P]ATP and the incorporation of 32P into nuclear protein was examined. 2. Liver nuclear proteins were phosphorylated to a much greater extent than those of muscle. Particularly low levels of phosphorylation were observed in white greater extent than those of muscle. Particularly low levels of phosphorylation were observed in white muscle nuclei. 3. Most of the phosphoproteins were common to all the tissues but significant quantitative differences and a limited number of qualitative differences were evident, particularly between liver and the muscle tissues. 4. Many phosphoproteins detected were minor components of the total nuclear protein.

Age changes of the isoelectric points of non-histone chromosomal proteins from rat liver in the pH range 5 to 8

Non-histone chromosomal proteins were extracted from purified nuclei of young (2-3 months) and old (24-28 months) rat liver by a two-phase partition method (chloroform:-isoamyl alcohol, 24:1) after histone depletion with 0.25N HCl. The proteins were subjected to analytical isoelectric focusing in the pH range 5-8. On the densitograms derived from Coomasie brilliant blue R-250 stained gels, there were formally four areas separated having the following pH ranges: I) 5.80-6.10; II) 6.25-6.42; III) 6.80-7.00; IV) 7.20-7.35 for young rats, and I) absent; II) 6.35-6.75; III) 6.80-7.00; IV) 7.12-7.40 for old rats. Hence, the main result is the absence of a group of proteins from old rats having the pH range 5.80-6.10. The factors involved in protein separation by isoelectric focusing, like time-dependent post-translational charge modifications: phosphorylation, acetylation, ADP-ribosylation, deamidation, terminal peptide cleavage, glycosylation, and DNA-like contaminants are discussed.

Effect of heme on globin messenger RNA synthesis in spleen erythroid cells

Synthesis of globin mRNA in erythroid spleen cells from anemic mice was measured after in vitro incubation under conditions in which the level of intracellular heme was manipulated. This newly synthesized globin mRNA was isolated by hybridization with globin cDNA covalently bound to cellulose. Isonicotinic acid hydrazide (INH) and penicillamine were used as specific inhibitors of heme synthesis. It has been found that a 120-min incubation of spleen erythroid cells with 5mM INH or 5mM penicillamine reduced [3H] uridine incorporation into globin mRNA by 24% or 36%, respectively. The addition of heme to INH- or penicillamine-treated cells almost completely restored [3H] uridine incorporation into globin mRNA. These results indicate that heme stimulates transcription of processing of globin mRNA.

Electron-microscopic X-ray microanalysis of normal and diseased human muscle

Electron-microscopic X-ray microanalysis has been used to compare elemental concentrations in specific organelles in normal and diseased human muscle. An elevated calcium to phosphorus ratio has been found in both myonuclei and interstitial cell nuclei in diseased muscle compared with controls. Preliminary observations also suggest that differences in elemental concentrations may be associated with structural abnormalities such as internal nuclei, and loss of myofibrils.