Identification of A1 protein as the fourth member of 13 kDa-type acidic ribosomal protein family in yeast Saccharomyces cerevisiae

The identity of protein A1 predicted by a cDNA clone from yeast Saccharomyces cerevisiae which has common carboxyl-terminus to 13 kDa-type acidic ribosomal proteins has been examined. The unique gene for A1 was isolated using the cDNA clone and found to possess two boxes similar to upstream activation sequences for ribosomal protein genes (UASrpg) in the 5'-flanking region. The in vitro-translation product directed by hybrid-selected mRNA with A1 cDNA comigrated with a minor component of split proteins from ribosome by electrofocusing. In addition, the mRNA level for A1 was found to be lower than other two major acidic ribosomal proteins suggesting that A1 is the fourth member of the protein family so far identified which is expressed at relatively low level.

On the size and the role of a free cytosolic pool of acidic ribosomal proteins in yeast Saccharomyces cerevisiae

A small but distinct amount of yeast acidic ribosomal proteins A1/A2 was detected in cytosol by immunoblotting on a two-dimensional gel electrophoretogram, while 38 kDa acidic protein A0 was not detected. The free forms of A1/A2 in the cytosol were eluted in gel filtration at the molecular mass of about 30 kDa under non-denaturation conditions, suggesting that they exist as a dimer or timer without association with A0. The amount of free A1/A2 was determined by immunoblotting to be 0.3% of the ribosome-bound A1/A2 in yeast. The time course of incorporation of radioactive amino acid showed that the cytosolic free A1/A2 are labeled more rapidly with high specific radioactivity than the ribosome-bound A1/A2. This result suggested that some of the cytosolic A1/A2, if not all, are newly-synthesized proteins which are ready for incorporation into cytoplasmic ribosomes.

Protease-nicked theta-toxin of Clostridium perfringens, a new membrane probe with no cytolytic effect, reveals two classes of cholesterol as toxin-binding sites on sheep erythrocytes

A nicked theta-toxin (C theta), obtained by limited proteolysis with subtilisin Carlsberg, causes almost no hemolysis while it retains a nearly intact cholesterol binding site below 20 degrees C. Neither electron microscopic evidence for the formation of arc- and ring-shaped structures on the membrane nor toxin-stimulated influx of extracellular Ca2+ are detected in C theta-treated cells below 20 degrees C. Thus, event(s) in the lytic process are responsible for the temperature dependency of hemolysis, which is also supported by the observation that C theta requires higher Arrhenius activation energy for hemolysis than the native toxin. Using C theta as a probe due to its high affinity for membrane cholesterol without causing any obvious membrane changes, we demonstrated the possible existence of high- and low-affinity sites for theta-toxin on sheep erythrocytes. Both binding sites disappear by simultaneous treatment of the cells with sublytic doses of digitonin. Furthermore, C theta binds only to cholesterol among the chloroform/methanol-extractable, lipid components of sheep and human erythrocytes but not to the protein components derived from them. These results strongly suggest that cholesterol is an essential component of the both high- and low-affinity sites, and also imply that the modes of existence of cholesterol in the red cell membrane are heterogeneous.

Complete purification and immunochemical analysis of S-adenosylmethionine synthetase from bovine brain

We have purified S-adenosylmethionine (AdoMet) synthetase about 3000-fold from bovine brain extract. The Km values of the enzyme for L-methionine and ATP were 10 and 50 microM, respectively. An apparent molecular mass of the enzyme was estimated to be 160 kDa by gel filtration on a Sephacryl S-200 column. Sucrose density gradient centrifugation gave a sedimentation coefficient of 8 S. Polyacrylamide gel electrophoresis of the purified enzyme in native system revealed a single protein band, whereas two polypeptide bands with molecular masses of 48 kDa (p48) and 38 kDa (p38) were observed in sodium dodecyl sulfate-polyacrylamide gel electrophoresis of the purified enzyme. Antibody against bovine brain AdoMet synthetase was prepared by injecting the purified enzyme into a rabbit. Immunoblot analysis revealed that the antibody recognized both p48 and p38 in the impure enzyme preparations from bovine brain as well as in the purified enzyme. Specific antibodies against p48 and p38 were separated from the immunoglobulin fraction by an affinity purification, both of which inhibited the enzyme activity. These results indicate that AdoMet synthetase from bovine brain consists of two different polypeptides, p48 and p38.

The metabolism of ribosomal proteins microinjected into the oocytes of Xenopus laevis

When the total proteins from Xenopus laevis 60 S ribosomal subunits (TP60) were 3H-labeled in vitro and injected back into X. laevis oocytes, most 3H-TP60 are integrated into the cytoplasmic 60 S subunits via the nucleus during 16 h of incubation. In the oocytes whose rRNA synthesis is inhibited, 3H-TP60 are rapidly degraded with a half-life of 2-3 h. This degradation ceased as soon as rRNA synthesis was resumed, suggesting that ribosomal proteins unassociated with nascent rRNA are unstable in the oocytes. The degradation of 3H-TP60 in the absence of RNA synthesis was inhibited by iodoacetamide, a cysteine protease inhibitor, resulting in the accumulation of 3H-TP60 in the nucleus reaching about a threefold concentration in the cytoplasm. Considering the results with enucleated oocytes, we suggest that the X. laevis nucleus has a limited capacity to accumulate ribosomal proteins in an active manner but that those ribosomal proteins accumulated in excess over rRNA synthesis are degraded by a cysteine protease in the nucleus. By contrast, ribosomal proteins from Escherichia coli only equilibrate between the nucleus and the cytoplasm and are degraded by serine protease(s) in the cytoplasm without being integrated in the form of ribosomes in the nucleus.

Characterization of a novel acidic protein of 38 kDa, A0, in yeast ribosomes which immunologically cross-reacts with the 13 kDa acidic ribosomal proteins, A1/A2

A new ribosomal protein of 38 kDa, named A0, was detected in yeast ribosomes on immunoblotting. The antibody used here was that against A1/A2, 13 kDa acidic ribosomal proteins which cross-reacted with A0. Although A0 and A1/A2 share common antigenic determinants, they differ in the following biochemical properties. While A1/A2 could be extracted from ribosomes with ethanol and ammonium sulfate, A0 could not. A0 gave two protein spots in a less acidic region than for A1/A2 on two-dimensional gel electrophoresis. The heterogeneity observed for A0 was ascribable to phosphorylation because one spot disappeared after treatment of the ribosomes with phosphatase. The syntheses of A0 and A1/A2 are directed by different mRNA species, as judged with a cell-free translation system, ruling out the possibility that A0 is a precursor of A1/A2. Although a mammalian ribosomal protein equivalent to A0 has been shown to be associated with 13 kDa acidic proteins in the cytoplasm, essentially no A0 was detected on immunoblotting in the yeast cytosol, while a small but detectable amount of A1/A2 was present. The possibility that A0 is a eukaryotic equivalent of L10 of Escherichia coli is discussed.

[Effects of pathological synovial fluids on the metabolism of chondrocytes]

The purpose of this study was to clarify the mechanism of joint destruction in rheumatoid arthritis and osteoarthritis by observing the effects of the pathological synovial fluids on proteoglycan (PG) and collagen metabolism of chondrocytes. When chondrocytes from chick embryo were cultured with pathological synovial fluids, especially RA synovial fluid, biosynthesis of both proteoglycan and collagen of chondrocytes were found to increase in proportion to the amounts of pathological synovial fluids applied to the culture medium. Chondrocytes began to synthesize PG of small molecular size, approximately 70,000 in addition to PG of normal molecular size. It is noteworthy that the PG of small molecular size shows a shortening of the glycosaminoglycan link and core protein on undersulfation. These findings indicate that pathological synovial fluids disturb the biochemical regulation of the articular cartilage matrix by altering both PG and collagen metabolisms of chondrocytes.

The mechanism of action of ricin and related toxic lectins on eukaryotic ribosomes. The site and the characteristics of the modification in 28 S ribosomal RNA caused by the toxins

Ricin is a potent cytotoxic protein derived from the higher plant Ricinus communis that inactivates eukaryotic ribosomes. In this paper we have studied the mechanism of action of ricin A-chain on rat liver ribosomes in vitro. Our findings indicate that the toxin inactivates the ribosomes by modifying both or either of two nucleoside residues, G4323 and A4324, in 28 S rRNA. These nucleotides are located close to the alpha-sarcin cleavage site and become resistant to all ribonucleases tested. The examination of the lability of phosphodiester bonds of these nucleotides to both mild alkaline digestion and aniline treatment at acidic pH suggests that the base of A4324 is removed by the toxin. This unique activity of ricin A-chain was also observed when naked 28 S rRNA is used as a substrate, indicating that the toxin directly acts on the RNA. Similar activity on 28 S rRNA is also exhibited by abrin and modeccin, ricin-related toxins, suggesting a general mechanistic pathway for ribosome inactivation by lectin toxins.

Cold-labile hemolysin produced by limited proteolysis of theta-toxin from Clostridium perfringens

A nicked toxin whose hemolytic activity is temperature dependent was obtained by limited proteolysis of theta-toxin (Mr 54,000) with subtilisin. The nicked toxin (C theta) is a complex of two fragments: the N-terminal fragment (Mr 15,000) with basic isoelectric point and the C-terminal fragment (Mr 39,000) with the single cysteinyl residue of the toxin whose reduced form is essential for the hemolytic activity. C theta hemolyzes erythrocytes only at temperatures above 25 degrees C, whereas the native toxin hemolyzes them even at 10 degrees C. At temperatures below 25 degrees C, C theta does not hemolyze them although it does bind to membrane cholesterol and although no distinct difference was observed between the secondary structure of C theta and that of native toxin. It was found that C theta binds to the cells only in a reversible manner at low temperature, while the native one binds irreversibly to the cells within 10 min, which explains the cold lability of C theta on hemolysis. The structural basis of the cold lability was discussed through comparison of C theta with another nicked derivative of theta-toxin that was also obtained.

Detection and partial characterization of the chromatin-associated proteases of yeast Saccharomyces cerevisiae

The chromatin fraction was prepared from yeast Saccharomyces cerevisiae free from cytoplasmic contamination except for a trace of mitochondria. When the yeast chromatin was incubated with histones as a substrate it showed three peaks of proteolytic activity as approximately pH 4, pH 7 and pH 11. These activities were separated from each other by differential extractions from chromatin and successive gel filtration through Sephadex G-100. Proteases were partially characterized by affinity labeling with [3H]diisopropylfluorophosphate (iPr2P-F) and by various protease inhibitors. The neutral and the alkaline proteases were serine proteases with a molecular mass of 35 kDa and 25 kDa respectively. The acidic protease showed a molecular size larger than 100 kDa on the gel filtration, and was probably an aspartyl protease because it was most strongly inhibited by pepstatin. A iPr2P-F-binding protein with a molecular mass of 66 kDa, found in chromatin, was likely to be converted to the alkaline protease of 25 kDa when chromatin was incubated at pH 10 or in 6 M urea/0.1 M phosphoric acid at the extraction. The distribution of proteolytic activities and iPr2P-F-binding proteins were compared among chromatins from different strains and from cells in different growth phases and it was found that these three proteases were present in all of them but with different proportions. Considering that rat liver chromatin contains equivalents to these proteases [Tsurugi, K. and Ogata, K. (1982) J. Biochem. (Tokyo) 92, 1369-1381], the results suggested that they play some important roles in the function of eukaryotic chromatin.

Activation of phosphatidic acid metabolism of human erythrocyte membranes by perfringolysin O

The effect of perfringolysin O on the lipid metabolism of human erythrocyte membranes was investigated. Erythrocytes were prelabeled with [3H]arachidonic acid and [32P]inorganic phosphate. In the presence of calcium ion(5.5 mM), the effect of perfringolysin O on lipid metabolism was very similar to that of an calcium-ionophore A23187. In the absence of calcium ion, the accumulation of phosphatidic acid and its following decreasing trend were observed during the reaction with the toxin. Such changes were not caused by filipin. These results suggest that perfringolysin O causes the activation of a diglyceride-phosphatidic acid cycle, which might be involved in the calcium transport.

Effects of ethylenediaminetetraacetic acid and gentamicin on the antibacterial activity of pyridone carboxylic acid derivatives against gram-negative bacilli

Ofloxacin (9-fluoro-3-methyl-10-(4-methyl-1-piperazynyl)-7-oxo-2,3-dihydro-7 H-pyrido-(1,2,3-de)1,4-benzoxazine-6-carboxylic acid) and enoxacin (1-ethyl-6-fluoro-1,4-dehydro-4-oxo-7-(1-piperazinyl)-1, 8-naphthyridine-3-carboxylic acid) are newly developed pyridone carboxylic acid derivatives with broad and potent antibacterial activities against Gram-negative and Gram-positive bacteria. Antibacterial activities of six pyridone carboxylic acid derivatives, including these two new antibiotics, were examined against Gram-negative bacilli in the presence and absence of ethylenediaminetetraacetic acid (EDTA) or gentamicin. The minimal inhibitory concentrations (MICs) of nalidixic acid, cinoxacin and piromidic acid were reduced by the addition of EDTA or gentamicin. However, the MICs of pipemidic acid, ofloxacin and enoxacin were unaffected. These findings indicated the high permeability of pipemidic acid, ofloxacin and enoxacin through the outer membrane. The effects of EDTA and gentamicin against Serratia marcescens were different from those against other Gram-negative bacilli.

Restoration by recombinant interferon alpha A/D of host defense systems against tumor in immunosuppressed mice

Recombinant human interferon alpha A/D (alpha A/D) restored or augmented host defense systems against tumors in immunosuppressed mice. In normal C57BL/6 mice, inoculation of B16 melanoma F1 cells caused few pulmonary metastasis, whereas in mice pretreated with cyclophosphamide (CY) it caused a high incidence of pulmonary metastasis, leading to earlier death than in the normal mice inoculated with the same dose of the tumor. alpha A/D given after the CY treatment counteracted the deleterious effects of the CY treatment. Since such restorative activity was seen even against the subline of B16 F1 which had been made resistant to its direct antiproliferative effect, alpha A/D seems to exert its effect indirectly through host defense systems. However, this activity of alpha A/D in the mice pretreated with CY was abrogated by inoculation of anti-asialo GM1 serum but not by i-carrageenan. The CY treatment reduced NK activity, while alpha A/D given after the CY treatment restored or augmented the NK cell activity in lung cells and peripheral blood mononuclear cells, but not in spleen cells. These findings suggest that the restoration or augmentation of NK activity in the lung and/or peripheral blood might be the major factor leading to the antimetastatic activity of alpha A/D in the mice treated with CY.