Evidence for the synthesis in vivo of proteins of the Calvin cycle and of the photosynthetic electron-transfer pathway on chloroplast ribosomes

Ferredoxin:NADP oxidoreductase of Cyanophora paradoxa: purification, partial characterization, and N-terminal amino acid sequence

The ferredoxin:NADP+ oxidoreductase of the protist Cyanophora paradoxa, as a descendant of a former symbiotic consortium, an important model organism in view of the Endosymbiosis Theory, is the first enzyme purified from a formerly original endocytobiont (cyanelle) that is found to be encoded in the nucleus of the host. This cyanoplast enzyme was isolated by FPLC (19% yield) and characterized with respect to the uv-vis spectrum, pH optimum (pH 9), molecular mass of 34 kDa, and an N-terminal amino acid sequence (24 residues). The enzyme shows, as known from other organisms, molecular heterogeneity. The N-terminus of a further ferredoxin:NADP+ oxidoreductase polypeptide represents a shorter sequence missing the first four amino acids of the mature enzyme.

Biosynthesis of ribulose-1.5-bisphosphate carboxylase in greening cells of Euglena gracilis : The accumulation of ribulose-1.5-bisphosphate carboxylase and of its subunits

Light induction of chloroplast development in Euglena leads to quantitative changes in the protein composition of the soluble cell part. One major part of these is the observed accumulation of ribulose-1.5-bisphosphate carboxylase/oxygenase (RuBPCase) enzyme (EC 4.1.1.39). As measured by immunoelectrophoresis, a small amount of RuBPCase (about 10(-6) pmol) is present in a dark-grown cell, whereas a greening cell (72h) contains 10-20 pmol enzyme. Both the cytoplasmic and chloroplastic translation inhibitors, cycloheximide and spectinomycin, have a strong inhibitory effect on the synthesis of the enzyme throughout the greening process of Euglena cells. Electrophoretic and immunological analyses of the soluble phase prepared from etiolated or greening cells do not show the presence of free subunits of the enzyme. For each antibiotic-treated greening cell, the syntheses of both subunits are blocked. Our data indicate that tight reciprocal control between the syntheses of the two classes of subunits occurs in Euglena. In particular, the RuBPCase small subunit synthesis in greening Euglena seems more dependent on the protein synthesis activity of the chloroplast than the syntheses of other stromal proteins from cytoplasmic origin.

Synthesis of thylakoid membrane proteins by chloroplasts isolated from spinach. Cytochrome b559 and P700-chlorophyll a-protein

Intact chloroplasts, purified from spinach leaves by sedimentation in density gradients of colloidal silica, incorporate labeled amino acids into at least 16 different polypeptides of the thylakoid membranes, using light as the only source of energy. The thylakoid products of chloroplast translation were visualized by subjecting membranes purified from chloroplasts labeled with [35S]methionine to electrophoresis in high-resolution, SDS-containing acrylamide gradient slab gels and autoradiography. The apparent mol wt of the labeled products ranged from less than 10,000 to greater than 70,000. One of the labeled products is the apoprotein of the P700-chlorophyll a-protein (CPI). The CPI apoprotein is assembled into a pigment-protein complex which is electrophoretically indistinguishable from the native CPI complex. Isolated spinach chloroplasts also incorporate [3H]leucine and [35S]methionine into cytochrome b559. The radioactive label remains with the cytochrome through all stages of purification: extraction of the thylakoid membranes with Triton X-100 and urea, adsorption of impurities on DEAE cellulose, two cycles of electrophoresis in Triton-containing polyacrylamide gels and electrophoresis in SDS-containing gradient gels. Cytochrome b559 becomes labeled with both [3H]leucine and [35S]methionine and accounts for somewhat less than 1% of the total isotopic incorporation into thylakoid protein. The lipoprotein appears to be fully assembled during the time-course of our labeling experiments.

Ribulose bisphosphate carboxylase from a mutant strain of Chlamydomonas reinhardii deficient in chloroplast ribosomes : The absence of both subunits and their pattern of synthesis during enzyme recovery

The ac-20 mutant strain of the unicellular green alga, Chlamydomonas reinhardii, lacks both chloroplast ribosomes and ribulose bisphosphate carboxylase activity when grown on organic medium. Under these conditions, the cells do not posses pools of either the large or small subunit of this enzyme. When transferred to inorganic medium, the carboxylase activity recovers. During this recovery, de novo synthesis of both subunits occurs. Synthesis of both subunits is inhibited by chloramphenicol even when possible free subunit pools rather than just the subunits incorporated into whole enzyme are examined.

Ribosomal RNA genes in the nucleus and chloroplast of Euglena

Centrifugation of DNA from Euglena gracilis in Hg2+-CS2SO4 equilibrium gradients allows the chloroplast DNA to be separated clearly from the nuclear DNA. Cytoplasmic ribosomal RNA isolated from a heat-bleached strain hybridizes only to the nuclear DNA. The ribosomal RNA cistrons in the chloroplast DNA are not related to those in the nuclear DNA. A possible origin for the chloroplast genome is suggested by the observation that roughly one-fourth of the ribosomal RNA complementary sequences in chloroplast DNA anneal with RNA from the blue-green alga Anacystis nidulans.

Composition, quaternary structure, and catalytic properties of D-ribulose-1, 5-bisphosphate carboxylase from Euglena gracilis

D-Ribulose-1,5-bisphosphate carboxylase has been purified in one step by sedimenting extracts of autotrophically-grown Euglena gracilis into a linear 0.2-0.8 M sucrose density gradient. The resultant product was pure by the criteria of disc electrophoresis in gels polymerized from 5 or 7.5% acrylamide and sedimentation. The molecular weight of the enzyme estimated by density gradient centrifugation and electrophoresis in gels polymerized from various concentrations of acrylamide was 5.25 X 10(5). The S20,W was 16.4 S. Dissociation and polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulphate established that the enzyme was composed of two types of subunits (mr 50,000 and 15,000). The oligomeric structure was visualized through negative staining and transmission electron microscopy leading to a model for the quaternary structure. Although the enzyme was moderately unstable, the estimated maximal specific activity was 1.6 mumol CO2 fixed min-1 mg protien-1 at 30 degrees C and pH 8.0 Km values were 2.2 m M, 15. 1 MUM and 0.63 mM for Mg2+, ribulose 1,5-bisphosphate, and CO2, respectively, when measured under air. 6-Phospho-D-gluconate was a noncompetitive inhibitor with respect to ribulose 1,5-bisphosphate (Ki = 0.04 mM). Oxygen was a competitive inhibitor with respect to CO2 suggesting that the enzyme was also an oxygenase. The latter was confirmed by experiments showing a molar equivalence between ribulose-1,5-bisphosphate-dependent oxygen consumption and phosphoglycerate production.

Vitamin B12 and the macromolecular composition of Euglena. 3. Effect of cycloheximide on the recovery from B12-induced unbalanced growth

When cycloheximide is added to (B12)-deficient cultures before or after replenishment of the cells with B(12), reversion of these cells is inhibited. This inhibition is not caused by interference of the inhibitor in the uptake of B(12) as measured by division kinetics. Cycloheximide does not inhibit the initial increase in the rate of DNA synthesis caused by B(12) replenishment, but within 30-45 min the rate decreases and DNA synthesis ceases. Cycloheximide added to replenished deficient cells after completion of DNA duplication inhibits cell division. The total cellular protein and RNA in replenished cells treated with cycloheximide does not change. B(12) added to deficient cells does not stimulate the incorporation of [(14)C]leucine into protein during resumption and completion of DNA duplication. However, there is a large increase in [(14)C]leucine incorporation into the protein of these cells soon after completion of DNA duplication and before resumption of cell division. The addition of cycloheximide to B(12)-replenished or to nonreplenished deficient cells rapidly inhibits the incorporation. We suggest that the addition of B(12) accelerates the rate of DNA synthesis in the deficient cells and that possibly no new protein synthesis is required except for mitosis. However, protein synthesis is needed for continuous DNA synthesis.

A possible ribosomal-directed regulatory system in Euglena gracilis. Chlorophyll synthesis

Cycloheximide at concentrations of 0.1-100mum stimulated chlorophyll synthesis when dark-grown cells of Euglena were illuminated. Chloramphenicol (1-4mm) inhibited chlorophyll synthesis. The effect of cycloheximide on the incorporation of [(14)C]leucine into material insoluble in trichloroacetic acid, and its failure to affect the incorporation of [(32)P]orthophosphate into such material in short incubations, are interpreted as evidence that cycloheximide specifically inhibits protein synthesis by 80S ribosomes. Since the inhibitory effect of chloramphenicol on chlorophyll synthesis is counteracted by the presence of cycloheximide, it is suggested that chlorophyll synthesis is subject to control by a cytoplasmic repressor synthesized on 80S ribosomes, and to a de-repressor synthesized on 70S ribosomes.

Role of light in the synthesis of nitrate reductase and nitrite reductase in rice seedlings

1. In rice seedlings synthesis of methyl viologen-nitrite reductase was stimulated by light, as was that of NADH-nitrate oxidoreductase (EC 1.6.6.1). A small residual effect of light on the synthesis of the enzymes persisted in the dark for a short time. 2. In etiolated seedlings exposed to light and nitrate, a lag period of 3h was necessary before enzyme synthesis commenced, whereas in green seedlings kept in the dark for 36h, synthesis of both the enzymes started as soon as light and nitrate were provided. 3. Experiments with cycloheximide suggested that fresh protein synthesis in light was necessary for formation of active enzymes. Mere activation by light of inactive enzymes or their precursors, was not involved. 4. In green seedlings synthesis of nitrite reductase was more sensitive to chloramphenicol than that of nitrate reductase. In chloramphenicol-treated etiolated seedlings, however, synthesis of both the enzymes was inhibited to the same extent on subsequent light-treatment. 5. A close correlation was observed between inhibition of the Hill reaction by 3-(3,4-dichlorophenyl)-1,1-dimethylurea and simazin [2-chloro-4,6-bis(ethylamino)-s-triazine] (at high concentration) and the inhibition of enzyme synthesis. At lower concentrations, however, simazin stimulated nitrate reductase. 6. In a single leaf synthesis of enzymes was observed only in portions exposed to light, whereas little activity was present in the dark covered part. 7. CO(2) deprivation severely inhibited the synthesis of enzymes in the light. Sucrose could not reverse this effect. 8. In excised embryos cultured in synthetic media containing sucrose, light was also essential for enzyme formation. 9. It is suggested that redox changes taking place in the green tissues as a result of the Hill reaction create conditions favourable for the induced synthesis of nitrate reductase and nitrite reductase.

Effects of chloramphenicol on chloroplast and mitochondrial ultrastructure in Ochromonas danica

The effect of chloramphenicol (CAP) on cell division and organelle ultrastructure was studied during light-induced chloroplast development in the Chrysophyte alga, Ochromonas danica. Since the growth rate of the CAP-treated cells is the same as that of the control cells for the first 12 hr in the light, CAP is presumed to be acting during that interval solely by inhibiting protein synthesis on chloroplast and mitochondrial ribosomes. CAP markedly inhibits chloroplast growth and differentiation. During the first 12 hr in the light, chlorophyll synthesis is inhibited by 93%, the formation of new thylakoid membranes is reduced by 91%, and the synthesis of chloroplast ribosomes is inhibited by 81%. Other chloroplast-associated abnormalities which occur during the first 12 hr and become more pronounced with extended CAP treatment are the presence of prolamellar bodies and of abnormal stacks of thylakoids, the proliferation of the perinuclear reticulum, and the accumulation of dense granular material between the chloroplast envelope and the chloroplast endoplasmic reticulum. CAP also causes a progressive loss of the mitochondrial cristae, which is paralleled by a decline in the growth rate of the cells, but it has no effect on the synthesis of mitochondrial ribosomes. We postulate that one or more chloroplast ribosomal proteins are synthesized on chloroplast ribosomes, whereas mitochondrial ribosomal proteins are synthesized on cytoplasmic ribosomes.

Structure and function in the euglenoid eyespot apparatus: The fine structure, and response to environmental changes

The microanatomy of the eyespot apparatus of Euglena gracilis Z was examined with the electron microscope. The stigma was found to be a membrane-bounded organelle showing no close homology with the chloroplast or any other organelle. The structure and pigment content of the stigma both diminish with extended hetrotrophic growth, and quickly regain normal dimensions upon exposure to light. Synthesis of the red pigment is particularly sensitive to inhibition by chloramphenicol, whereas construction of the structure itself is specifically inhibited by cycloheximide.The paraflagellar body appears to consist of two sets of parallel 80 Å striations intersecting at 60°. It is within the flagellar membrane, but separated from the axoneme by another structure, the paraflagellar rod. This elongated structure has an ordered substructure which appears as intersecting sets of parallel striations; part of its basal portion projects as a circular flange which makes contact with the paraflagellar body.

A major polypeptide of chloroplast membranes of Chlamydomonas reinhardi. Evidence for synthesis in the cytoplasm as a soluble component

Electrophoresis of thylakoid membrane polypeptides from Chlamydomonas reinhardi revealed two major polypeptide fractions. But electrophoresis of the total protein of green cells showed that these membrane polypeptides were not major components of the cell. However, a polypeptide fraction whose characteristics are those of fraction c (a designation used for reference in this paper), one of the two major polypeptides of thylakoid membranes, was resolved in the electrophoretic pattern of total protein of green cells. This polypeptide could not be detected in dark-grown, etiolated cells. Synthesis of the polypeptide occurred during greening of etiolated cells exposed to light. When chloramphenicol (final concentration, 200 microg/ml) was added to the medium during greening to inhibit chloroplastic protein synthesis, synthesis of chlorophyll and formation of thylakoid membranes were also inhibited to an extent resulting in levels of chlorophyll and membranes 20-25% of those found in control cells. However, synthesis of fraction c was not affected by the drug. This polypeptide appeared in the soluble fraction of the cell under these conditions, indicating that this protein was synthesized in the cytoplasm as a soluble component. When normally greening cells were transferred from light to dark, synthesis of the major membrane polypeptides decreased. Also, it was found that synthesis of both subunits of ribulose 1, 5-diphosphate carboxylase was inhibited by chloramphenicol, and that synthesis of this enzyme stopped when cells were transferred from light to dark.

[Structure and function of the genetic information in plastids : V. The absence of ribosomal rna from the plastids of the plastom-mutant 'mrs. parker' of Pelargonium zonale]

1. The variety 'Mrs. Parker' of Pelargonium zonale (fig. 1) is a periclinal chimera of the constitution white-over-green (LI and L II: white, L III: green). Reciprocal crosses with the green variety 'Trautlieb' demonstrate a biparental, extranuclear inheritance of the character green.- white. The F1 consists of green, green-white variegated and white seedlings (table 1). 2. In green-white variegated F1-plants "mixed cells" (fig. 2) have been found containing two genetically different types of plastids: green plastids (from 'Trautlieb') and white plastids (from 'Mrs. Parker'). The white cells of 'Mrs. Parker' represent a white plastid mutant (= plastom mutant); its genetic designation is "extranuclear: alba-1", symbol en: alba-1. 3. Leaf material for biochemical studies was obtained from pure white and entirely green shoots of variegated F1 hybrids (fig. 3). The ultrastructure of the white plastids was studied by electron microscopy. 4. From normal green cells of Pelargonium zonale four bands of high molecular weight ribosomal RNA can be isolated: 25 S and 18 S RNA of the cytoplasmic ribosomes and 23 S and 16 S RNA of plastid ribosomes (fig. 5a). 5. The mutation of the plastid DNA in the plastids of 'Mrs. Parker' causes an altered RNA pattern: The 23 S and 16 S RNA of the plastid ribosomes cannot be detected in polyacrylamid gels (whereas 25 S and 18 S RNA are present) (fig. 5b). 6. In cells of white leaves numerous plastids are present. They are smaller than normal chloroplasts and have a double-layered envelope. However, the formation of normal internal membrane structures is blocked. 7. In mutated plastids of 'Mrs. Parker' ribosomes cannot be detected in electron micrographs (fig. 6). 8. From these findings we conclude that protein synthesis cannot be performed in mutated plastids. The multiplication of the plastids - and presumably also the replication of plastid DNA - is not impaired by the deficiency in plastid protein synthesis. 9. These results indicate that protein synthesis within the plastids is necessary for full development and differentiation of the chloroplasts, although an essential part of the plastidal proteins are synthesized on cytoplasmic ribosomes.

The intracellular localization of glycollate oxidoreductase in Euglena gracilis

1. Lowering of the concentration of carbon dioxide in air available to phototrophically growing Euglena cultures from 5% to the normal value (0.03%) resulted in an increased specific activity of glycollate oxidoreductase. 2. The effects of chloramphenicol and cycloheximide suggested that this increase in activity was due to enzyme synthesis de novo on cytoplasmic ribosomes. 3. The K(m) for glycollate oxidation by the enzyme in crude cell extracts was 3.0x10(-3)m. 4. Differential centrifugation established that glycollate oxidoreductase present in phototrophically grown Euglena is a particulate enzyme. The enzyme was partially solubilized by the non-ionic detergent Triton X-100. 5. Sucrose-density-gradient centrifugation achieved the separation of the particulate glycollate oxidoreductase from chloroplasts and mitochondria. 6. Glutamate-glyoxylate aminotransferase was associated with particulate glycollate oxidoreductase.

The effects of inhibitors of RNA and protein synthesis on chloroplast structure and function in wild-type Chlamydomonas reinhardi

Wild-type cells of the unicellular green alga Chlamydomonas reinhardi have been grown for several generations in the presence of rifampicin, an inhibitor of chloroplast DNA-dependent RNA polymerase, spectinomycin and chloramphenicol, two inhibitors of protein synthesis on chloroplast ribosomes, and cycloheximide, an inhibitor of protein synthesis on cytoplasmic ribosomes. The effects of cycloheximide are complex, and it is concluded that this inhibitor cannot give meaningful information about the cytoplasmic control over the synthesis of chloroplast components in long-term experiments with C. reinhardi. In the presence of acetate and at the appropriate concentrations, the three inhibitors of chloroplast protein synthesis retard growth rates only slightly and do not affect the synthesis of chlorophyll; however, photosynthetic rates are reduced fourfold after several generations of growth. Each inhibitor produces a similar pattern of lesions in the organization of chloroplast membranes. Only rifampicin prevents the production of chloroplast ribosomes.

[Influence of rifampicin, chloramphenicl and cycloheximide on uridine-incorporation into chloroplast ribosome precursors of Chlorella]

The unicellular green alga Chlorella incorporates labeled uridine mainly into the precursors of chloroplast ribosomes. After treatment with rifampicin for 60 min, the uridine incorporation into the particles is completely inhibited. Chloramphenicol treatment results in the same complete inhibition. In constrast, cycloheximide (actidione) slightly stimulates the incorporation of uridine into the chloroplast ribosome precursors.Short-time incorporation of inorganic phosphate into the ribosome fractions is nearly unaffected by rifampicin and chloramphenicol, but it is strongly inhibited by cycloheximide.Isolation and chromatographic separation of nucleic acids after treatment of cells with rifampicin shows that uridine incorporation into RNA is completely inhibited. Chloramphenicol causes only partial inhibition of uridine labeling in the high molecular weight RNA. Here again, cycloheximide stimulates the uridine incorporation.The results indicate that uridine is preferentially incorporated by Chlorella cells into the chloroplast ribosome precursors. Inorganic phosphate is introduced both into cytoplasmic and into chloroplasmic RNA, but because of the quantitative distribution, the cytoplasmic ribosomes are more extensively labeled. Since only inhibitors of bacterial and chloroplasmic RNA-and protein synthesis affect the formation of uridine-labeled ribosomes, this synthesis must take place in the chloroplast itself.