The acidic ribosomal phosphoprotein of eukaryotes and its relationship to ribosomal proteins L7 and L12 of Escherichia coli

The ribosomal proteins phosphorylated in vitro by protein kinase activities from Krebs II ascites cells

Studies were performed to identify in cytoplasmic extracts of Krebs II ascites cells protein kinase activities that might be responsible for the phosphorylation of the ribosomal proteins previously identified as phosphoproteins in these cells in vivo. Column chromatography resolved a casein kinase activity that could use ATP or GTP as a phosphoryl donor to phosphorylate, in ribosomes, exclusively the acidic 60S phosphoprotein(s) phosphorylated in vivo. A second casein kinase fraction could use ATP, only, in a similar reaction, but also contained protein kinase activity with respect to other ribosomal proteins, including the basic ribosomal protein phosphorylated in vivo, ribosomal protein S6. This latter was also among several proteins phosphorylated by an activity in the cyclic AMP-independent histone kinase fraction.

Ribosomal acidic proteins of eucaryotic cells. Isolation of a protein from pea seedlings equivalent to E. coli L7/L12

By the method of ethanol-salt extraction with ion-exchange chromatography on CM-cellulose an acidic protein of pea 80S ribosomes was isolated. This protein located in the large subunit, had a molecular weight of 14 000 and an IEP of 4.7. The protein is partially phosphorylated, alanine-rich and has methionine at the N-terminal position. Based on these characteristics and on the comparative study of tryptic hydrolyzates of the plant protein and E. coli L7/L12, the protein so obtained is found to be homologous to the L7/L12 of the procaryotic ribosomes.

The protein synthetic activity in vitro of ribosomes differing in the extent of phosphorylation of their ribosomal proteins

We describe a re-examination of the cell-free protein synthetic activity of eukaryotic ribosomes having proteins phosphorylated to different extents. Ribosomal 40 S subunits were isolated both from a variety of cells in which there is relatively little phosphorylation of ribosomal protein S6, and from cells subjected in vivo to different stimuli that promote the extensive phosphorylation of protein S6. The ability of these subunits to bind Met-tRNA as well as the second amino acyl-tRNA (Val-tRNA) was compared in the presence of highly purified initiation factors, elongation factor EF-1 at various concentrations of 60S subunits, 9 S globin mRNA and potassium ions. The ability of the subunits to synthesize polyphenylalanine was also studied using highly purified elongation factors. In no case was any significant difference in activity observed between ribosomes with protein S6 phosphorylated to different extents. Similar, though less extensive, studies were preformed comparing 60 S ribosomal subunits differing in the extent of phosphorylation of the acidic phosphoprotein, L gamma , and of L14. No difference in activity was observed between these ribosomes.

Ribosomal core-particles as the target of ricin

Core-particles and split-proteins were prepared by treatment with ethanol and NH4Cl of control and ricin-treated Artemia salina ribosomes. No modifications of the ricin-treated split-proteins was detected by polyacrylamide-gel electrophoresis. Moreover, the split-proteins from ricin-treated ribosomes complemented control core-particles in poly(U)-directed phenylalanine polymerization. Conversely, ricin-treated core-particles remained totally inactive when supplemented with control split-proteins.

Resistance of the peptidyltransferase centre of rabbit ribosomes to attack by nucleases and proteinases

Larger ribosomal subparticles (L-subparticles) of rabbit ribosomes were treated with either ribonucleases (I or T1) or proteinases (trypsin or chymotrypsin), and their capacity to function in poly(U)-directed polyphenylalanine synthesis and in the puromycin reaction was investigated. The effects of pretreatment of L-subparticles on the reconstruction of active subparticles from core-particles derived by treatment with 2.75 M-NH4Cl/69 mM-MgCl2 and split-protein fractions were also examined. The protein moiety of proteinase-treated L-subparticles was analysed by one-dimensional sodium dodecyl sulphate/polyacrylamide- and two-dimensional polyacrylamide-gel electrophoresis. The introduction of 16--100 scissions in the RNA moiety had no effect on the activity of the L-subparticles in polyphenylalanine synthesis, and there was no effect on the stability of L-subparticles to high-salt shock treatment and a marginal effect on the reconstruction of L-subparticles from high-salt-shock core-particles and split-protein fractions. In contrast, L-subparticles treated with low amounts of trypsin (0.56 ng of trypsin/microgram of L-subparticle) were inactive in polyphenylalanine synthesis, and their capacity to function in partial-reconstruction experiments was diminished. Activity in the puromycin reaction was increased by 70% as a result of trypsin treatment (280 ng of trypsin/microgram of L-subparticle). At least two of the acidic proteins implicated in the translocation function were not affected by trypsin treatment. Trypsin-treated L-subparticles had lost their capacity to bind the smaller ribosomal subparticle (S-subparticle). The protein(s) needed for S-subparticle binding were shown to be present in high-salt-shock cores. At least six proteins associated with the core-particles were attack during trypsin treatment of L-subparticles. An examination of L-subparticles isolated from trypsin-treated polyribosomes showed that the amount of trypsin necessary to decrease the activity of the subparticle by 50% was about twice that needed in the treatment of L-subparticles alone. The largest protein of rabbit L-subparticles (approx. 51 000 daltons) was cleaved in a stepwise fashion by trypsin to fragments of approx. 40 000 daltons. This protein was also cleaved by chymotrypsin.

Studies on ribosomal proteins in the cellular slime mold Dictyostelium discoideum. Resolution, nomenclature and molecular weights of proteins in the 40-S and 60-S ribosomal subunits

This study is concerned with the identification and subunit localization of ribosomal proteins in Dictyostelium discoideum. The characterization is based on the resolution of ribosomal proteins by various methods of electrophoresis. 34 and 42 unique proteins were identified in the 40-S and 60-S ribosomal subunits respectively. The total mass of proteins in the 40-S subunit was 746,100 daltons and 981,900 daltons in the 60-S subunit. The molecular weights of individual proteins in the 40-S subunit ranged from 13,200 to 40,900 with a number-average molecular weight of 21,900. The molecular weight range for the 60-S subunit was 13,800--51,100 with a number-average molecular weight of 23,400. The 80-S ribosome contained 78 proteins, two of which were lost upon its dissociation into subunits. All the proteins of the 40-S and 60-S subunits could be identified individually in a 80-S map as well as in unfractionated proteins from whole cells. Purification of ribosomes in high-ionic-strength buffers resulted in non-specific loss of the various proteins from the 40-S and 60-S subunits. In addition, the undissociated ribosomes contained about 10 acidic proteins in the molecular weight range 50,000--100,000, which were retained after washing the ribosomes in high-salt buffers. They were found in polysomes, run-off ribosomes and could also be identified in the 40-S subunit after dissociation.

Ribosomal protein modifications in liver injury: effect of carbon tetrachloride and extrahepatic cholestasis on protein phosphorylation

The phosphorylation of ribosomal proteins in rat liver injured fro various times by carbon tetrachloride and extrahepatic cholestasis was studied. The incorporation of [32P]phosphate into the protein moiety of the small ribosomal subunit was increased over 2-fold 1 to 4 h after injection of the hepatotoxin, whereas the specific activity of the 60 S subunit was low and changed only insignificantly. Two-dimensional electrophoretic analysis of ribosomal proteins complemented by autoradiography revealed that CCl4 stimulated the phosphorylation of only a single protein (S6) in the 40 S subunit. The phosphorylation of S6 led to a measurable anodic shift and elongation of the protein on the 2-dimensional electropherograms. In response to bile duct ligation a similar increase in phosphorylation of protein S6 was noticed.