Studies on proteins of animal ribosomes. XIV. Analysis of phosphorylated rat liver ribosomal proteins by two-dimensional polyacrylamide gel electrophoresis

Comparison of phosphorylation of ribosomal proteins from HeLa and Krebs II ascites-tumour cells by cyclic AMP-dependent and cyclic GMP-dependent protein kinases

Phosphorylation of eukaryotic ribosomal proteins in vitro by essentially homogeneous preparations of cyclic AMP-dependent protein kinase catalytic subunit and cyclic GMP-dependent protein kinase was compared. Each protein kinase was added at a concentration of 30nM. Ribosomal proteins were identified by two-dimensional gel electrophoresis. Almost identical results were obtained when ribosomal subunits from HeLa or ascites-tumour cells were used. About 50-60% of the total radioactive phosphate incorporated into small-subunit ribosomal proteins by either kinase was associated with protein S6. In 90 min between 0.7 and 1.0 mol of phosphate/mol of protein S6 was incorporated by the catalytic subunit of cyclic AMP-dependent protein kinase. Of the other proteins, S3 and S7 from the small subunit and proteins L6, L18, L19 and L35 from the large subunit were predominantly phosphorylated by the cyclic AMP-dependent enzyme. Between 0.1 and 0.2 mol of phosphate was incorporated/mol of these phosphorylated proteins. With the exception of protein S7, the same proteins were also major substrates for the cyclic GMP-dependent protein kinase. Time courses of the phosphorylation of individual proteins from the small and large ribosomal subunits in the presence of either protein kinase suggested four types of phosphorylation reactions: (1) proteins S2, S10 and L5 were preferably phosphorylated by the cyclic GMP-dependent protein kinase; (2) proteins S3 and L6 were phosphorylated at very similar rates by either kinase; (3) proteins S7 and L29 were almost exclusively phosphorylated by the cyclic AMP-dependent protein kinase; (4) protein S6 and most of the other proteins were phosphorylated about two or three times faster by the cyclic AMP-dependent than by the cyclic GMP-dependent enzyme.

Phosphorylation in vitro and in vivo of ribosomal proteins from Saccharomyces cerevisia

Crude ribosomes from Saccharomyces cerevisiae cultures were phosphorylated in vitro when incubated in the presence of [gamma-32P]ATP. Analysis of the ribosomal proteins with two-dimensional electrophoresis revealed that of the 29 proteins identified in the small subunit, only protein S6 was phosphorylated. Of the 37 proteins identified in the large subunit, one was highly phosphorylated (L3) and two only slightly phosphorylated (L11 and L14). The protein kinase activity associated with the ribosomes was extracted with 1 M KCl and was not dependent on adenosine 3':5'-monophosphate; it preferentially phosphorylated casein and phosvitin, but was less active on histones. Structural ribosomal proteins were also phosphorylated in vivo when the yeast cultures were incubated with [32P]orthophosphate; the radioactivity resistant to hydrolysis by hot perchloric acid was incorporated into the proteins of the two subunits. Radioactive phosphoserine was found by subjecting hydrolysates of ribosomal proteins to high-voltage electrophoresis. After two-dimensional electrophoresis, one poorly phosphorylated protein (S10) was identified in the small subunit. In the large subunit, one protein (L3) was highly labelled, and two proteins (L11 and L24) only slightly labelled.

Characterisation of eukaryotic ribosomal proteins

A simple method of two-dimensional polyacrylamide gel electrophoresis is described which affords: (1) high resolution of eukaryotic ribosomal proteins; (2) good recovery of protein in the transfer from first to second dimension; and (3) characterisation of the separated proteins in terms of molecular weights and other electrophoretic properties. Using this method, we have characterised 70 proteins in rabbit reticulocyte ribosomes, 30 from the small subunit and 40 from the large subunit. The molecular weight distribution is compared with those obtained by other authors after fractionation of the proteins in two dimensions.

Ribosomal protein as substrate for a GTP-dependent protein kinase from yeast

A protein kinase specific for casein and acidic ribosomal proteins was isolated and partly characterized. It was found that the enzyme utilizes GTP and ATP as phosphoryl donors. Its affinity for ATP was considerably higher than for GTP with the km values of 7.6 X 10(-6)M and 5.5 X 10(-5)M, respectively. Two-dimensional acrylamide gel electrophoresis revealed the phosphorylation of the same ribosomal proteins with either of the [gamma-32P] nucleotides used. It was also shown that one acidic protein (S1 or S2) of 40 S and two acidic proteins (L2 and L3) of 60 S ribosomal subunits were predominantly phosphorylated in vitro. The phosphorylated proteins: L2 and L3 seem to correspond to the proteins of L7 and L12 of E. coli ribosomes. The isolated kinase phosphorylated several basic ribosomal proteins though to a lower extent than the acidic ones.

Phosphorylation of ribosomal proteins from eukaryotes in homologous and heterogous cell-free systems

The phosphorylation of ribosomal proteins from eukaryotes in homologous and heterologous cell-free systems has been studied. The ribosomes and protein kinases from yeast (Saccharomyces cerevisiae, strain Bu), wheat (Triticum vulgare) and rabbit (Orystolagus cuniculus) have been used. It has been found that five ribosomal proteins incorporate gamma-32P from ATP during the incubation of wheat ribosomes with wheat protein kinase. When the phosphorylation of isolated wheat ribosomal proteins was examined more phosphoproteins were detected. These data confirm the suggestion that the ribosomal structure affects the phosphorylation. Probably some ribosomal proteins remain hidden for the action of protein kinase. The results from the crossed experiments show that there is no barrier for phosphorylation of yeast ribosomes with liver protein kinase, of wheat ribosomes with yeast and liver protein kinases and of liver ribosomes with yeast and plant protein kinases. The wheat protein kinase does not phosphorylate the yeast ribosomes under these experimental conditions. Some differences in the set of phosphoproteins obtained with various protein kinases have been detected. These data suggest that the ribosomal protein phosphorylation is not highly species specific although it is not universal.

Analysis by two-dimensional polyacrylamide gel electrophoresis of the in vivo phosphorylation of ribosomal proteins derived from free and membrane-bound polysomes

Analysis of in vivo phosphorylation of mouse liver ribosomal proteins was performed by two-dimensional polyacrylamide gel electrophoresis following 32P-injection. Our method is special and differs from other eukaryotic systems reported in that all proteins separated on the first dimension gel are completely solubilized, moving quantitatively to the second dimension gel. Only ribosomes from polysomes were used, ensuring analysis of ribosomes actively engaged in protein synthesis. We resolved sixty-five distinct proteins from ribosomes from membrane bound or free polysomes. In both cases radioautography revealed similar labeled patterns with one highly phosphorylated ribosomal protein and five marginally labeled spots.

Study of mammalian ribosomal protein reactivity in situ. II. - Effect of glutaraldehyde and salts

Results concerning ribosomal protein sensitivity to glutaraldehyde were compared to protein depletion studies using LiCl centrifugation. The relative degree of reactivity of the different proteins was determined by two-dimensional acrylamide gel electrophoresis, and the activity of the reacted subunits was measured. The results obtained mostly confirmed the studies of methoxynitrotropone reactivity reported earlier. For example, L16, L25, L29, L30, L31, S18, S20 appeared to be definitely exposed to both NH2-reagents and LiCl. Some interesting points emerged from this study regarding protein topography in both subunits: (1) with few exceptions, almost all ribosomal proteins were accessible to the surrounding medium; (2) the sensitivity of the 40S proteins to the three reagents used was lower than was that of the 60S proteins; (3) the reactivities of the subunit components changed when subunits were associated: L8 was more reactive with glutaraldehyde in 60S subunits than in 80S ribosomes. In contrast, S14, S15 and S19 were more exposed in ribosomes than in the 40S subunits.

Changes in the reactivity of proteins of rat liver ribosomes against [14Ciodoacetamide depending on their organization in ribosomal subparticles, 80S ribosomes and on the attachment of poly-(U)

(1) The isolated mixtures of ribosomal proteins can be substituted by [14C]-iodoacetamide up to an average of about 2 equivalents per 20,000 dalton. The extent of substitution of single proteins measured after two-dimensional polyacrylamide gel electrophoresis shows that all proteins are reactive. (2) Also in the subunits, all proteins are accessible to substitution. Compared with isolated proteins, however, the reactivity is decreased and the amount of labelling for most proteins ranges as low as 5 to 20%. (3) Reassociation of ribosomal subunits decreases the reactivity of 12 proteins of the small subunit and that of 20 proteins of the large subunit. (4) The presence of messenger inhibits the substitution of 10 proteins of the small subunit and of 6 proteins of the large one. (5) Seven proteins of the small subunit and 3 proteins of the large one are influenced both by the other subunit and by messenger-RNA.