Isolation and Characterization of the Acidic Phosphproteins of 60-S Ribosomes from Artermia salina and Rat Liver (original) (raw)

The acidic ribosomal proteins as regulators of the eukaryotic ribosomal activity

… et Biophysica Acta (BBA …, 1990

The acidic proteins, A-proteins, from the large ribosomal subunit of Saccharomyces cerevisiae grown under different conditions have been quantitatively estimated by ELISA tests using rabbit sera speclfic for these polypeptides. It has been found that the amount of A-protein present in the ribosome is not constant and depends on the metabolic state of the cell. Ribosomes from exponentially growing cultures have about 40% more of these proteins than those from stationary phase. Similarly, the particles forming part of the polysomes are enriched in A-proteins as compared with the free 80 S ribosomes. The cytoplasmic pool of A-protein is considerably high, containing as a whole as much protein as the total ribosome population. These results are compatible with an exchanging process of the acidic proteins during protein synthesis that can regulate the activity of the ribosome. On the other hand, cells inhibited with different metabolic inhibitors produce a very low yield of ribosomes that contain, however, a surprisingly high amount of acidic proteins while the cytoplasmic pool is considerably reduced, suggesting that under stress conditions the ribosome and the A-protein may aggregate, forming complex structures that are not recovered by the standard preparation methods.

Acidic Ribosomal Proteins from Eukaryotic Cells. Effect on Ribosomal Functions

European Journal of Biochemistry, 1979

Precipitation of Saccharomyces cerevisiae ribosomes by ethanol under experimental conditions that do not release the ribosomal proteins can affect the activity of the particles. In the presence of 0.4 M NH4Cl and 50% ethanol only the most acidic proteins from yeast and rat liver ribosomes are released. At 1 M NH4Cl two more non-acidic proteins are lost from the ribosomes. The release of the acidic proteins causes a small inactivation of the polymerizing activity of the particles, additional to that caused by the precipitation itself. The elongation-factor-2-dependent GTP hydrolysis of the ribosomes is, however, more affected by the loss of acidic proteins. These proteins can stimulate the GTPase but not the polymerising activity when added back to the treated particles. Eukaryotic proteins cannot be sustituted for bacterial acidic proteins L7 and L12. We have not detected immunological cross-reaction between acidic proteins from Escherichia coli and those from yeast, Artemia salina and rat liver or between acidic proteins from these eukaryotic ribosomes among themselves.

The acidic proteins of eukaryotic ribosomes A comparative study

Biochimica et Biophysica Acta (BBA) - Nucleic Acids and Protein Synthesis, 1981

The acidic proteins extracted by 0.4 M NH4CI and 50% ethanol from ribosomes from Saccharomyces cerevisiae, wheat germ, Artemia salina, Drosophila melanogaster, rat liver and rabbit reticulocytes have been studied comparatively in several structural and functional aspects. All the species studied have in the ribosome two strongly acidic proteins with pl values not greater than pH 4.5, which appear to be monophosphorylated in the case of S. cerevisiae, A. salina, D. melanogaster and wheat germ. Rat liver proteins are multiphosphorylated, as possibly are those from reticulocytes. The molecular weight of these acidic proteins as determined by SDS electrophoresis ranges from around 13 500 to 17000 and, except in the case of yeast, of which both proteins have the same molecular weight, the size of the two proteins in the other species differs by approx. 1000-2000. In general, the size of the proteins increases with the evolutionary position of the organism, as seems to be the case with the degree of phosphorylation. From an immunological point of view the ribosomal acidic proteins of eukaryotic cells are partially related, since antisera against yeast protein cross-react with proteins from wheat germ, rat liver and reticulocytes. Bacterial proteins L7 and L12 are very weakly recognized by the anti-yeast sera. Anti-bacterial acidic proteins do not cross-react with any of the protein from the species studied. The proteins from all the species studied are functional equivalents and can reconstitute the activity of particles of S. cerevisiae deprived of their acidic proteins.

Functional Roles of 50-S Ribosomal Proteins

European Journal of Biochemistry, 1977

Ribosomal proteins previously inactivated by treatment with fluorescein isothiocyanate have been incorporated into 50-S ribosomal subunits during reconstitution from particles disassembled by 2 M LiCl in the presence of an excess of the modified proteins. The reconstituted particles show alterations in some functional activities resulting from the incorporation of the inactive ribosomal proteins added exogenously. Of the fluorescein-isothiocyanate-treated proteins incorporated, L24 and L25 drastically affect all the activities tested and these proteins possibly play a fundamental role in determining the overall structure of the particle. Proteins L16 and LIO are apparently involved both in the GTP hydrolysis dependent on elongation factor G and in peptidyl transferase activity but the modified protein L11 only affects GTPase activity indirectly and interferes with the ribosome assembly process involving proteins L7 and L12. Protein L1 may be involved with peptidyl transferase activity while proteins L7 and L12, in agreement with many reports in the literature, affect the factor-dependent hydrolysis of GTP.

The primary structure of rat ribosomal protein L18a

FEBS Letters, 1989

The amino acid sequence of rat ribosomal protein L18a was deduced from the sequence of nucleotides in a recombinant cDNA. Ribosomal protein L18a contains 175 ammo acids and has a molecular mass of 20047 Da. Hybridization of the cDNA to digests of rat nuclear DNA and to a preparation of poly(A)+ mRNA suggests that there are 8-l 1 copies of the L18a gene and that the mRNA for the protein is about 700 nucleotides in length. Rat L18a is related to Schizosaccharomycespombe L17 and perhaps to Halobacterium marismortui L19.