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102
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Pfannschmidt T. Chloroplast redox signals: how photosynthesis controls its own genes. TRENDS IN PLANT SCIENCE 2003; 8:33-41. [PMID: 12523998 DOI: 10.1016/s1360-1385(02)00005-5] [Citation(s) in RCA: 281] [Impact Index Per Article: 13.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/21/2023]
Abstract
The photosynthetic apparatus of higher plants and algae is composed of plastid- and nuclear-encoded components, therefore the expression of photosynthesis genes needs to be highly coordinated. Expression is regulated by various factors, one of the most important of which is light. Photosynthesis functions as a sensor for such light signals, and the redox state of photosynthetic electron transport components and redox-active soluble molecules act as regulating parameters. This provides a feedback response loop in which the expression of photosynthesis genes is coupled to the function of the photosynthetic process, and highlights the dual role of photosynthesis in energy fixation and the reception of environmental information.
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Affiliation(s)
- Thomas Pfannschmidt
- Department of Plant Physiology, Friedrich-Schiller University of Jena, Dornburger Str. 159, Germany.
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103
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Abstract
Oxidation can damage all biological macromolecules, and the survival of a cell therefore depends on its ability to control the level of oxidants. Microbes possess an astonishing variety of antioxidant defences, ranging from small, oxidant-scavenging molecules to self-regulating, homeostatic gene networks. Most often these antioxidant defences are activated by exposure to specific classes of oxidants. Interestingly, the isolation of pleiotropic mutations that impair or exacerbate the expression of subsets of oxidant-responsive genes led to the identification of global regulators. In a few, well-characterized cases, these regulators can transduce oxidative damage into gene regulation. Recently, the application of genomic tools to study the antioxidant responses of E. coli has both confirmed previous observations and provided evidence for a wealth of putative new anti-oxidant functions. Here, we review the remarkable diversity of antioxidant defence mechanisms, with emphasis on signal transduction by global regulator proteins and the corresponding genetic networks that protect the microbial cell against oxidative stress.
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Affiliation(s)
- Pablo J Pomposiello
- Department of Cancer Cell Biology, Harvard School of Public Health, Boston, MA 02115, USA
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104
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Kim J, Mayfield SP. The active site of the thioredoxin-like domain of chloroplast protein disulfide isomerase, RB60, catalyzes the redox-regulated binding of chloroplast poly(A)-binding protein, RB47, to the 5' untranslated region of psbA mRNA. PLANT & CELL PHYSIOLOGY 2002; 43:1238-43. [PMID: 12407204 DOI: 10.1093/pcp/pcf129] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/20/2023]
Abstract
RB60, a chloroplast protein disulfide isomerase, modulates the binding of RB47, chloroplast poly(A)-binding protein, to the 5'-UTR of the psbA mRNA using redox potential, allowing for a reversible switch capable of regulating psbA mRNA translation in a light/dark dependent manner. RB60 contains two thioredoxin-like domains with putative catalytic sites of -Cys-Gly-His-Cys- that are presumed to function as active sites for the redox-regulated changes in RNA-binding activity of RB47. To investigate whether these motifs are required for redox-regulated RNA binding, RNA-gel-mobility shift assays were performed with RB47 and mutant RB60 proteins with single cysteines changed to serines in the -Cys-Gly-His-Cys- motif. The results showed that each thioredoxin-like domain has independent catalytic function in the reactivation of RB47 binding and that a double active site mutant completely lacks the ability to activate RB47 RNA binding activity.
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Affiliation(s)
- Jungmook Kim
- Department of Cell Biology and the Skaggs Institute for Chemical Biology, the Scripps Research Institute, 10550 North Torrey Pines Rd., La Jolla, CA 92037, U.S.A.
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105
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Schmidt M, Dehne S, Feierabend J. Post-transcriptional mechanisms control catalase synthesis during its light-induced turnover in rye leaves through the availability of the hemin cofactor and reversible changes of the translation efficiency of mRNA. THE PLANT JOURNAL : FOR CELL AND MOLECULAR BIOLOGY 2002; 31:601-613. [PMID: 12207650 DOI: 10.1046/j.1365-313x.2002.01382.x] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
Abstract
The enzyme catalase is light-sensitive. In leaves, losses caused by photoinactivation are replaced by new enzyme and the rate of de novo synthesis must be rapidly and flexibly attuned to fluctuating light conditions. In mature rye leaves, post-transcriptional mechanisms were shown to control the rate of catalase synthesis. The amount of the leaf catalase (CAT-1) transcript did not increase with light intensity, but was even higher after dark exposure of light-grown leaves. Initiation was apparently not limiting translation in the dark, as the association of the Cat1 mRNA with polysomes did not change notably under different light conditions. By analysing the translation of catalase polypeptides in cell-free systems with poly(A)+ RNA from leaves or with mRNA transcribed from a Cat1-containing cDNA clone, two mechanisms of post-transcriptional control were identified. First, translation of catalase depended on the presence of hemin. In leaves, the availability of hemin may signal the extent of catalase degradation as the hemin of the inactivated enzyme is recycled. Second, the translation efficiency of the Cat1 transcripts was reversibly modulated in a dose-dependent manner by the light intensity to which leaves were exposed, prior to extraction. The Cat1 mRNA from light-exposed leaves was translated much more efficiently than mRNA from dark-exposed leaves. The increase of its translation activity in vivo was not blocked by cordycepin but was suppressed by methylation inhibitors, indicating a reversible modification of pre-existing mRNA by methylation. Translation of in vitro synthesized Cat1 mRNA required a methylated cap (m7GpppG), but was virtually below detection when it contained an unmethylated cap (GpppG).
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Affiliation(s)
- Matthias Schmidt
- Botanisches Institut, Goethe-Universität, PO Box 11 19 32, D-60054 Frankfurt am Main, Germany
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106
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Auchincloss AH, Zerges W, Perron K, Girard-Bascou J, Rochaix JD. Characterization of Tbc2, a nucleus-encoded factor specifically required for translation of the chloroplast psbC mRNA in Chlamydomonas reinhardtii. J Cell Biol 2002; 157:953-62. [PMID: 12045185 PMCID: PMC2174033 DOI: 10.1083/jcb.200201060] [Citation(s) in RCA: 58] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/15/2002] [Revised: 04/30/2002] [Accepted: 04/30/2002] [Indexed: 11/22/2022] Open
Abstract
Genetic analysis has revealed that the three nucleus-encoded factors Tbc1, Tbc2, and Tbc3 are involved in the translation of the chloroplast psbC mRNA of the eukaryotic green alga Chlamydomonas reinhardtii. In this study we report the isolation and phenotypic characterization of two new tbc2 mutant alleles and their use for cloning and characterizing the Tbc2 gene by genomic complementation. TBC2 encodes a protein of 1,115 residues containing nine copies of a novel degenerate 38-40 amino acid repeat with a quasiconserved PPPEW motif near its COOH-terminal end. The middle part of the Tbc2 protein displays partial amino acid sequence identity with Crp1, a protein from Zea mays that is implicated in the processing and translation of the chloroplast petA and petD RNAs. The Tbc2 protein is enriched in chloroplast stromal subfractions and is associated with a 400-kD protein complex that appears to play a role in the translation of specifically the psbC mRNA.
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Affiliation(s)
- Andrea H Auchincloss
- Department of Molecular Biology and Department of Plant Biology, University of Geneva, 1211 Geneva 4, Switzerland
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107
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Katz YS, Danon A. The 3'-untranslated region of chloroplast psbA mRNA stabilizes binding of regulatory proteins to the leader of the message. J Biol Chem 2002; 277:18665-9. [PMID: 11904302 DOI: 10.1074/jbc.m201033200] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The 5'-leader and 3'-tail of chloroplast mRNAs have been suggested to play a role in posttranscriptional regulation of expression of the message. The regulation is thought to be mediated, at least in part, by regulatory proteins that are encoded by the nuclear genome and targeted to the chloroplast where they interact with chloroplast mRNAs. Previous studies identified high affinity binding of the 5'-untranslated region (UTR) of the chloroplast psbA mRNA by Chlamydomonas reinhardtii proteins. Here we tested whether the 3'-UTR of psbA mRNA alone or linked in cis with the 5'-UTR of the mRNA affects the high affinity binding of the message in vitro. We did not detect high affinity binding that is unique to the 3'-UTR. However, we show that the cis-linked 3'-UTR increases the stability of the 5'-UTR binding complex. This effect could provide a means for translational discrimination against mRNAs that are incorrectly processed.
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Affiliation(s)
- Yael S Katz
- Department of Plant Sciences, Weizmann Institute of Science, Rehovot 76100, Israel
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108
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Zhang L, Aro EM. Synthesis, membrane insertion and assembly of the chloroplast-encoded D1 protein into photosystem II. FEBS Lett 2002; 512:13-8. [PMID: 11852043 DOI: 10.1016/s0014-5793(02)02218-4] [Citation(s) in RCA: 66] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
Rapid light-dependent turnover of the chloroplast-encoded D1 protein maintains photosystem II (PS II) functional over a wide range of light intensities. Following initiation of psbA mRNA translation, the elongating D1 is targeted, possibly by chloroplast signal recognition particle 54 (cpSRP54), to the thylakoid cpSecY translocation channel. Transmembrane domains of nascent D1 start interacting with other PS II core proteins already during the translocation process to ensure an efficient assembly of the multiprotein membrane complex. Here we review the progress recently made concerning the synthesis, targeting, membrane insertion and assembly to PS II of the chloroplast-encoded D1 protein and discuss the possible convergence of targeting and translocation of chloroplast- and nuclear-encoded thylakoid proteins.
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Affiliation(s)
- Lixin Zhang
- Department of Biology, University of Turku, FIN-20014, Turku, Finland
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109
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Mullineaux P, Karpinski S. Signal transduction in response to excess light: getting out of the chloroplast. CURRENT OPINION IN PLANT BIOLOGY 2002; 5:43-48. [PMID: 11788307 DOI: 10.1016/s1369-5266(01)00226-6] [Citation(s) in RCA: 138] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
Abstract
Plants are continually in danger of absorbing more light energy than they can use productively for their metabolism. Acclimation to environmental conditions therefore includes the development of mechanisms for dissipating or avoiding the accumulation of such excess excitation energy. Acclimation could be controlled by many signal transduction pathways that would be initiated by the perception of excess excitation energy both inside and outside the chloroplast. Recent studies in related areas provide models of how these signalling pathways could operate in acclimation to excess light. Components of photosynthetic electron transport chains, reactive oxygen species, redox-responsive protein kinases, thiol-regulated enzymes, chlorophyll precursors and chloroplast-envelope electron transport chains all have roles in these models.
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Affiliation(s)
- Philip Mullineaux
- Department of Disease and Stress Biology, John Innes Centre, Colney, NR4 7UH, Norwich, UK.
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110
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111
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Eichacker LA, Henry R. Function of a chloroplast SRP in thylakoid protein export. BIOCHIMICA ET BIOPHYSICA ACTA 2001; 1541:120-34. [PMID: 11750668 DOI: 10.1016/s0167-4889(01)00151-3] [Citation(s) in RCA: 51] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Protein export systems derived from prokaryotes are used to transport proteins into or across the endoplasmic reticulum, the mitochondrial inner membrane, and the chloroplast thylakoid membrane. Signal recognition particle (SRP) and its receptor are essential components used exclusively for cotranslational export of endomembrane and secretory proteins to the endoplasmic reticulum in eukaryotes and export of polytopic membrane proteins to the cytoplasmic membrane in prokaryotes. An organellar SRP in chloroplasts (cpSRP) participates in cotranslational targeting of chloroplast synthesized integral thylakoid proteins. Remarkably, cpSRP is also used to posttranslationally localize a subset of nuclear encoded thylakoid proteins. Recent work has begun to reveal the basis for cpSRP's unique ability to function in co- and posttranslational protein localization, yet much is left to question. This review will attempt to highlight these advances and will also focus on the role of other soluble and membrane components that are part of this novel organellar SRP targeting pathway.
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112
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Chen Q, Nussbaum-Shochat A, Amster-Choder O. A novel sugar-stimulated covalent switch in a sugar sensor. J Biol Chem 2001; 276:44751-6. [PMID: 11579106 DOI: 10.1074/jbc.m108729200] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The bgl sensory system is composed of a membrane-bound sugar sensor, BglF, and a transcriptional regulator, BglG. The sensor BglF has several enzymatic activities: in its nonstimulated state, it acts as BglG phosphorylase; in the presence of beta-glucoside in the growth medium, it acts as BglG dephosphorylase and as the beta-glucoside phosphotransferase. The same active site on BglF, Cys-24, is responsible for the phosphorylation of both the stimulating sugar and the BglG protein. BglF is composed of three domains, two hydrophilic and one hydrophobic. Our previous results suggested that catalysis of the sugar-stimulated functions depends on specific interactions between the B domain, which contains the active site cysteine, and the integral membrane C domain. We report here that the stimulating sugar triggers the formation of a disulfide bond between the active site cysteine and another cysteine in the membrane-embedded domain of BglF. Inability of a mutant BglF protein to form the disulfide bridge between the B and C domains correlates with its inability to catalyze the sugar-stimulated functions. The ability of the cysteine residue in BglF to bind covalently either to a phosphoryl group or to another cysteine residue, depending on the protein stimulation state, suggests a novel way to control signaling by alternative bond formation.
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Affiliation(s)
- Q Chen
- Department of Molecular Biology, The Hebrew University-Hadassah Medical School, P. O. Box 12272, Jerusalem 91120, Israel
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113
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Abstract
Oxidation of adjacent cysteine residues into a cystine forms a strained eight-membered ring. This motif was tested as the basis for an enzyme with an artificial redox switch. Adjacent cysteine residues were introduced into two different structural contexts in ribonuclease A (RNase A) by site-directed mutagenesis to produce the A5C/A6C and S15C/S16C variants. Ala5 and Ala6 are located in an alpha-helix, whereas Ser15 and Ser16 are located in a surface loop. Only A5C/A6C RNase A had the desired property. The catalytic activity of this variant decreases by 70% upon oxidation. The new disulfide bond also decreases the conformational stability of the A5C/A6C variant. Reduction with dithiothreitol restores full enzymatic activity. Thus, the insertion of adjacent cysteine residues in a proper context can be used to modulate enzymatic activity.
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Affiliation(s)
- C Park
- Department of Biochemistry, University of Wisconsin-Madison, Madison, WI 53706, USA
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114
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Petracek ME, Thompson WF. Post-transcriptional light regulation of nuclear-encoded genes. GENETIC ENGINEERING 2001; 22:1-10. [PMID: 11501372 DOI: 10.1007/978-1-4615-4199-8_1] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/21/2023]
Abstract
A significant number of studies have detected a post-transcriptional component in the light responses of nuclear genes. As yet there are few in-depth studies of the mechanism(s) involved, and it seems likely some additional examples have been missed. For instance, transcriptional responses have sometimes been inferred on the basis of experiments with translational fusions containing both the promoter and 5' UTR of the test gene, but we now know that elements within the 5' UTR can mediate post-transcriptional light responses. Similarly, because of possible changes in translation rates and protein turnover, the common assumption that mRNA levels directly dictate protein levels is tenuous at best. It is no longer permissible to assume that the biological effect of a gene is a simple function of its transcription. Thus it is likely that with careful experimental design, reports of nuclear-encoded post-transcriptional gene regulation will become increasingly prevalent.
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Affiliation(s)
- M E Petracek
- Department of Biochemistry and Molecular Biology, 246 Noble Research Center, Oklahoma State University, Stillwater, OK 74078, USA
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115
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Trebitsh T, Danon A. Translation of chloroplast psbA mRNA is regulated by signals initiated by both photosystems II and I. Proc Natl Acad Sci U S A 2001; 98:12289-94. [PMID: 11593046 PMCID: PMC59807 DOI: 10.1073/pnas.211440698] [Citation(s) in RCA: 81] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/18/2000] [Accepted: 08/16/2001] [Indexed: 11/18/2022] Open
Abstract
Light controls the translation of several mRNAs in fully developed chloroplasts via at least two regulatory pathways. In the first, the light signal is transduced as a thiol-mediated signal that modulates translation in parallel to light intensity. The second light-controlled pathway, termed priming, is a prerequisite to the thiol-mediated regulatory pathway. Light regulation is rapid and requires intrachloroplast photoreceptor(s). To delineate the signaling pathways controlling each of these regulatory events, we assayed the effect of photosynthetic inhibitors and electron donors on the translation of chloroplastic psbA mRNA. We show that the thiol-mediated signal is generated by photosystem I and transduced by vicinal dithiol-containing proteins. We also found that the priming signal probably initiates on reduction of plastoquinone. These findings suggest that translation of chloroplast psbA mRNA is controlled by both linear photosynthetic electron transport, exerted by the reduction of the ferredoxin-thioredoxin system, and the relative activities of photosystems I and II, signaled by the redox state of the plastoquinone pool. These data underscore the function of the light-capturing reactions of photosynthesis as chloroplast photoreceptors.
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Affiliation(s)
- T Trebitsh
- Department of Plant Sciences, Weizmann Institute of Science, Rehovot 76100, Israel
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116
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Abstract
Several plastid signals have been identified that regulate the transcription of nuclear genes for plastid and non-plastid proteins. These signals are related to the photosynthetic metabolism of chloroplasts and include porphyrins, reactive oxygen intermediates and carotenoids. The metabolic and developmental state of the chloroplast also control cell differentiation and leaf morphogenesis, but the signaling pathways have not been characterized. Plastid-to-nucleus and light-signaling pathways are separable in some but not all cases. Retrograde signaling thus plays a central role in coordinating gene expression in the nucleus, plastid and mitochondrion, and in integrating pathways of cellular metabolism and development.
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Affiliation(s)
- S Rodermel
- Department Botany, Iowa State University, 353 Bessey Hall, Ames, IA 50011, USA.
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117
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Daniell H, Streatfield SJ, Wycoff K. Medical molecular farming: production of antibodies, biopharmaceuticals and edible vaccines in plants. TRENDS IN PLANT SCIENCE 2001; 6:219-26. [PMID: 11335175 PMCID: PMC5496653 DOI: 10.1016/s1360-1385(01)01922-7] [Citation(s) in RCA: 385] [Impact Index Per Article: 16.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/18/2023]
Abstract
The use of plants for medicinal purposes dates back thousands of years but genetic engineering of plants to produce desired biopharmaceuticals is much more recent. As the demand for biopharmaceuticals is expected to increase, it would be wise to ensure that they will be available in significantly larger amounts, on a cost-effective basis. Currently, the cost of biopharmaceuticals limits their availability. Plant-derived biopharmaceuticals are cheap to produce and store, easy to scale up for mass production, and safer than those derived from animals. Here, we discuss recent developments in this field and possible environmental concerns.
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Affiliation(s)
- H Daniell
- Dept Molecular Biology and Microbiology and Center for Discovery of Drugs and Diagnostics, University of Central Florida, 12 722 Research Parkway, Orlando, FL 32826, USA.
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118
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Grossman AR, Bhaya D, He Q. Tracking the light environment by cyanobacteria and the dynamic nature of light harvesting. J Biol Chem 2001; 276:11449-52. [PMID: 11279225 DOI: 10.1074/jbc.r100003200] [Citation(s) in RCA: 129] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Affiliation(s)
- A R Grossman
- Department of Plant Biology, Carnegie Institution of Washington, Stanford, California 94305, USA.
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119
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Tyystjärvi T, Herranen M, Aro EM. Regulation of translation elongation in cyanobacteria: membrane targeting of the ribosome nascent-chain complexes controls the synthesis of D1 protein. Mol Microbiol 2001; 40:476-84. [PMID: 11309129 DOI: 10.1046/j.1365-2958.2001.02402.x] [Citation(s) in RCA: 85] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
The photosystem II reaction centre protein D1 is encoded by the psbA gene. The D1 protein is stable in darkness but undergoes rapid turnover in the light. Here, we show that, in cyanobacterium Synechocystis sp. PCC6803, the synthesis of the D1 protein is regulated at the level of translation elongation in addition to the previously known transcriptional regulation. When Synechocystis sp. PCC6803 cells were transferred from light to darkness, the psbA mRNA remained abundant for hours. Cytosolic ribosomes were attached to psbA transcripts in the dark, and translation continued up to a distinct pausing site. However, ribosome nascent D1 chain complexes were not targeted to the thylakoid membrane, and no full-length D1 protein was produced in darkness. The arrest in translation elongation was released in the light, concomitantly with targeting of ribosome D1 nascent-chain complexes to the thylakoid membrane, allowing the synthesis of the full-length D1 protein. Downregulation of membrane targeting of ribosome complexes was also observed in the light if damage to the D1 protein was slow. This novel type of regulation of prokaryotic translation functions to balance the synthesis and degradation of the rapidly turning over photosystem II D1 protein in Synechocystis sp. PCC6803.
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Affiliation(s)
- T Tyystjärvi
- Plant Physiology and Molecular Biology, University of Turku, BioCity A, Tykistökatu 6, FIN-20520 Turku, Finland.
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120
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Jiang D, Jha N, Boonplueang R, Andersen JK. Caspase 3 inhibition attenuates hydrogen peroxide-induced DNA fragmentation but not cell death in neuronal PC12 cells. J Neurochem 2001; 76:1745-55. [PMID: 11259492 DOI: 10.1046/j.1471-4159.2001.00151.x] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023]
Abstract
Exposure of neurons to H(2)O(2) results in both necrosis and apoptosis. Caspases play a pivotal role in apoptosis, but exactly how they are involved in H(2)O(2)-mediated cell death is unknown. We examined H(2)O(2)-induced toxicity in neuronal PC12 cells and the effects of inducible overexpression of the H(2)O(2)-scavenging enzyme catalase on this process. H(2)O(2) caused cell death in a time- and concentration-dependent manner. Cell death induced by H(2)O(2) was found to be mediated in part through an apoptotic pathway as H(2)O(2)-treated cells exhibited cell shrinkage, nuclear condensation and marked DNA fragmentation. H(2)O(2) also triggered activation of caspase 3. Genetic up-regulation of catalase not only significantly reduced cell death but also suppressed caspase 3 activity and DNA fragmentation. While the caspase 3 inhibitor DEVD inhibited both caspase 3 activity and DNA fragmentation induced by H(2)O(2) it did not prevent cell death. Treatment with the general caspase inhibitor ZVAD, however, resulted in complete attenuation of H(2)O(2)-mediated cellular toxicity. These results suggest that DNA fragmentation induced by H(2)O(2) is attributable to caspase 3 activation and that H(2)O(2) may be critical for signaling leading to apoptosis. However, unlike inducibly increased catalase expression and general caspase inhibition both of which protect cells from cytotoxicity, caspase 3 inhibition alone did not improve cell survival suggesting that prevention of DNA fragmentation is insufficient to prevent H(2)O(2)-mediated cell death.
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Affiliation(s)
- D Jiang
- Neurogerontology Division, Andrus Gerontology Center, University of Southern California, Los Angeles, California, USA
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121
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Trebitsh T, Meiri E, Ostersetzer O, Adam Z, Danon A. The protein disulfide isomerase-like RB60 is partitioned between stroma and thylakoids in Chlamydomonas reinhardtii chloroplasts. J Biol Chem 2001; 276:4564-9. [PMID: 11087734 DOI: 10.1074/jbc.m005950200] [Citation(s) in RCA: 42] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Translation of psbA mRNA in Chlamydomonas reinhardtii chloroplasts is regulated by a redox signal(s). RB60 is a member of a protein complex that binds with high affinity to the 5'-untranslated region of psbA mRNA. RB60 has been suggested to act as a redox-sensor subunit of the protein complex regulating translation of chloroplast psbA mRNA. Surprisingly, cloning of RB60 identified high homology to the endoplasmic reticulum-localized protein disulfide isomerase, including an endoplasmic reticulum-retention signal at its carboxyl terminus. Here we show, by in vitro import studies, that the recombinant RB60 is imported into isolated chloroplasts of C. reinhardtii and pea in a transit peptide-dependent manner. Subfractionation of C. reinhardtii chloroplasts revealed that the native RB60 is partitioned between the stroma and the thylakoids. The nature of association of native RB60, and imported recombinant RB60, with thylakoids is similar and suggests that RB60 is tightly bound to thylakoids. The targeting characteristics of RB60 and the potential implications of the association of RB60 with thylakoids are discussed.
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Affiliation(s)
- T Trebitsh
- Department of Plant Sciences, Weizmann Institute of Science, Rehovot 76100, Israel
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122
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McCormac DJ, Litz H, Wang J, Gollnick PD, Berry JO. Light-associated and processing-dependent protein binding to 5' regions of rbcL mRNA in the chloroplasts of a C4 plant. J Biol Chem 2001; 276:3476-83. [PMID: 11076953 DOI: 10.1074/jbc.m009236200] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
In amaranth, a C(4) dicotyledonous plant, the plastid rbcL gene (encoding the large subunit of ribulose-1,5-bisphosphate carboxylase) is regulated post-transcriptionally during many developmental processes, including light-mediated development. To identify post-transcriptional regulators of rbcL expression, three types of analyses (polysome heel printing, gel retardation, and UV cross-linking) were utilized. These approaches revealed that multiple proteins interact with 5' regions of rbcL mRNA in light-grown, but not etiolated, amaranth plants. Light-associated binding of a 47-kDa protein (p47), observed by UV cross-linking, was highly specific for the rbcL 5' RNA. Binding of p47 occurred only with RNAs corresponding to mature processed rbcL transcripts (5'-untranslated region (UTR) terminating at -66); transcripts with longer 5'-UTRs did not associate with p47 in vitro. Variations in the length of the rbcL 5'-UTR were found to occur in vivo, and these different 5' termini may prevent or enhance light-associated p47 binding, possibly affecting rbcL expression as well. p47 binding correlates with light-dependent rbcL polysome association of the fully processed transcripts in photosynthetic leaves and cotyledons but not with cell-specific rbcL mRNA accumulation in bundle sheath and mesophyll chloroplasts.
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Affiliation(s)
- D J McCormac
- Department of Biological Sciences, State University of New York, Buffalo, New York 14260, USA
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123
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124
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Proteins Involved in Biogenesis of the Thylakoid Membrane. REGULATION OF PHOTOSYNTHESIS 2001. [DOI: 10.1007/0-306-48148-0_9] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/13/2023]
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125
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126
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127
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Ossenbühl F, Nickelsen J. cis- and trans-Acting determinants for translation of psbD mRNA in Chlamydomonas reinhardtii. Mol Cell Biol 2000; 20:8134-42. [PMID: 11027283 PMCID: PMC86423 DOI: 10.1128/mcb.20.21.8134-8142.2000] [Citation(s) in RCA: 45] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Chloroplast translation is mediated by nucleus-encoded factors that interact with distinct cis-acting RNA elements. A U-rich sequence within the 5' untranslated region of the psbD mRNA has previously been shown to be required for its translation in Chlamydomonas reinhardtii. By using UV cross-linking assays, we have identified a 40-kDa RNA binding protein, which binds to the wild-type psbD leader, but is unable to recognize a nonfunctional leader mutant lacking the U-rich motif. RNA binding is restored in a chloroplast cis-acting suppressor. The functions of several site-directed psbD leader mutants were analyzed with transgenic C. reinhardtii chloroplasts and the in vitro RNA binding assay. A clear correlation between photosynthetic activity and the capability to bind RNA by the 40-kDa protein was observed. Furthermore, the data obtained suggest that the poly(U) region serves as a molecular spacer between two previously characterized cis-acting elements, which are involved in RNA stabilization and translation. RNA-protein complex formation depends on the nuclear Nac2 gene product that is part of a protein complex required for the stabilization of the psbD mRNA. The sedimentation properties of the 40-kDa RNA binding protein suggest that it interacts directly with this Nac2 complex and, as a result, links processes of chloroplast RNA metabolism and translation.
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Affiliation(s)
- F Ossenbühl
- Lehrstuhl für Allgemeine und Molekulare Botanik, Ruhr-Universität Bochum, 44780 Bochum, Germany
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128
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Abstract
The yeast transcription factor Yap1 activates expression of antioxidant genes in response to oxidative stress. Yap1 regulation involves nuclear accumulation, but the mechanism sensing the oxidative stress signal remains unknown. We provide biochemical and genetic evidence that upon H2O2 treatment, Yap1 is activated by oxidation and deactivated by enzymatic reduction with Yap1-controlled thioredoxins, thus providing a mechanism for autoregulation. Two cysteines essential for Yap1 oxidation are also essential for its activation by H2O2. The data are consistent with a model in which oxidation of Yap1 leads to disulfide bond formation with the resulting change of conformation masking recognition of the nuclear export signal by Crm1/Xpo1, thereby promoting nuclear accumulation of the protein. In sharp contrast to H2O2, diamide does not lead to the same Yap1 oxidized form and still activates mutants lacking cysteines essential for H2O2 activation, providing a molecular basis for differential activation of Yap1 by these oxidants. This is the first example of an H2O2-sensing mechanism in a eukaryote that exploits the oxidation of cysteines in order to respond rapidly to stress conditions.
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Affiliation(s)
- A Delaunay
- Service de Biochimie et de Génétique Moléculaire, DBCM, DSV, CEA-Saclay, Gif-sur-Yvette, 91191 Cedex, France.
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129
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Abstract
To cope with low nutrient availability in nature, organisms have evolved inducible systems that enable them to scavenge and efficiently utilize the limiting nutrient. Furthermore, organisms must have the capacity to adjust their rate of metabolism and make specific alterations in metabolic pathways that favor survival when the potential for cell growth and division is reduced. In this article I will focus on the acclimation of Chlamydomonas reinhardtii, a unicellular, eukaryotic green alga to conditions of nitrogen, sulfur and phosphorus deprivation. This organism has a distinguished history as a model for classical genetic analyses, but it has recently been developed for exploitation using an array of molecular and genomic tools. The application of these tools to the analyses of nutrient limitation responses (and other biological processes) is revealing mechanisms that enable Chlamydomonas to survive harsh environmental conditions and establishing relationships between the responses of this morphologically simple, photosynthetic eukaryote and those of both nonphotosynthetic organisms and vascular plants.
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130
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Tullberg A, Alexciev K, Pfannschmidt T, Allen JF. Photosynthetic electron flow regulates transcription of the psaB gene in pea (Pisum sativum L.) chloroplasts through the redox state of the plastoquinone pool. PLANT & CELL PHYSIOLOGY 2000; 41:1045-54. [PMID: 11100777 DOI: 10.1093/pcp/pcd031] [Citation(s) in RCA: 45] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
Abstract
Plants respond to changing light conditions by altering the stoichiometry between components of the photosynthetic electron transport chain of chloroplast thylakoids. We measured specific run-on transcription of the chloroplast genes psaB, psbA and rbcL in pea (Pisum sativum L.) seedlings grown under three different conditions of illumination: light selective for photosystem I (PSI-light); light selective for photosystem II (PSII-light); and a combination of PSI- and PSII-light (mixed light, ML). The transcriptional rate of the psaB gene increased under PSII-light and decreased under PSI-light, while the transcriptional rates of the psbA and rbcL genes were affected only in a non-specific way. Similar effects also occurred in plants grown under ML and switched to either PSI- or PSII-light for 4 h. Addition of the inhibitors of photosynthetic electron transport 3-(3,4 dichlorophenyl)-1,1-dimethylurea (DCMU) and 2,5-dibromo-3-methyl-6-isopropyl-p-benzoquinone (DBMIB) influenced psaB transcription in isolated, illuminated chloroplasts: DCMU addition resulted in oxidation of the plastoquinone pool and decreased transcription of psaB; DBMIB addition resulted in reduction of the plastoquinone pool and increased transcription of psaB. The experimental results obtained in vivo and in vitro provide evidence for coupling between the redox state of plastoquinone and the rate of transcription of the psaB gene in pea.
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Affiliation(s)
- A Tullberg
- Plant Cell Biology, Lund University, Sweden
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131
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Abstract
The conversion of genetic information stored in DNA into a protein product proceeds through the obligatory intermediate of messenger RNA. The steady-state level of an mRNA is determined by its relative synthesis and degradation rates, i.e., an interplay between transcriptional regulation and control of RNA stability. When the biological status of an organism requires that a gene product's abundance varies as a function of developmental stage, environmental factors or intracellular signals, increased or decreased RNA stability can be the determining factor. RNA stability and processing have long been known as important regulatory points in chloroplast gene expression. Here we summarize current knowledge and prospects relevant to these processes, emphasizing biochemical data. The extensive literature on nuclear mutations affecting chloroplast RNA metabolism is reviewed in another article in this volume (Barkan and Goldschmidt-Clermont, this issue).
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Affiliation(s)
- R A Monde
- Boyce Thompson Institute for Plant Research, Tower Rd., Cornell University, Ithaca, NY 14853, USA
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132
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Abstract
The expression of the plastid genome is dependent on a large number of nucleus-encoded factors. Some of these factors have been identified through biochemical assays, and many others by genetic screens in Arabidopsis, Chlamydomonas and maize. Nucleus-encoded factors function in each step in plastid gene expression, including transcription, RNA editing, RNA splicing, RNA processing, RNA degradation, and translation. Many of the factors discovered via biochemical approaches play general roles as components of the basic gene expression machinery, whereas the majority of those identified by genetic approaches are specifically required for the expression of small subsets of chloroplast genes and are involved in post-transcriptional steps. Some of the nucleus-encoded factors may play regulatory roles and modulate chloroplast gene expression in response to developmental or environmental cues. They may also serve to couple chloroplast gene expression with the assembly of the protein products into the large complexes of the photosynthetic apparatus. The convergence of biochemical approaches with those of classical and reverse genetics, and the contributions from large scale genomic sequencing should result in rapid advances in our understanding of the regulatory interactions that govern plastid gene expression.
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Affiliation(s)
- A Barkan
- Institute of Molecular Biology, University of Oregon, OR 97403, Eugene, USA
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133
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Abstract
The discovery that chloroplasts have semi-autonomous genetic systems has led to many insights into the biogenesis of these organelles and their evolution from free-living photosynthetic bacteria. Recent developments of our understanding of the molecular mechanisms of translation in chloroplasts suggest selective pressures that have maintained the 100-200 genes of the ancestral endosymbiont in chloroplast genomes. The ability to introduce modified genes into chloroplast genomes by homologous recombination and the recent development of an in vitro chloroplast translation system have been exploited for analyses of the cis-acting requirements for chloroplast translation. Trans-acting translational factors have been identified by genetic and biochemical approaches. Several studies have suggested that chloroplast mRNAs are translated in association with membranes.
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Affiliation(s)
- W Zerges
- Concordia University, 1455 de Maisonneuve W., H3G 1M8, Quebec, Montreal, Canada.
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134
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Irihimovitch V, Shapira M. Glutathione redox potential modulated by reactive oxygen species regulates translation of Rubisco large subunit in the chloroplast. J Biol Chem 2000; 275:16289-95. [PMID: 10821870 DOI: 10.1074/jbc.275.21.16289] [Citation(s) in RCA: 76] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Previous work showed a transient but dramatic arrest in the synthesis of Rubisco large subunit (LSU) upon transfer of Chlamydomonas reinhardtii cells from low light (LL) to high light (HL). Using dichlorofluorescin, a short-term increase in reactive oxygen species (ROS) was demonstrated, suggesting that their excessive formation could signal LSU down-regulation. A decrease in LSU synthesis occurred at LL in the presence of methyl viologen and was prevented at HL by ascorbate. Interfering with D1 function by mutations or by incubation with DCMU prevented the increase in ROS formation at HL and the concomitant down-regulation of LSU synthesis. If the electron transport was blocked further downstream, by mutation in the cytochrome b(6)/f or by incubation with 2, 5-dibromo-3-methyl-6-isopropyl-p-benzoquinone, ROS formation increased, and LSU synthesis ceased. The elevation of ROS occurred concurrently with a change in the redox state of the glutathione pool, which shifted toward its oxidized form immediately after the transfer to HL and returned to its original value after 6 h. The decrease in the reduced/oxidized glutathione ratio at HL was prevented by ascorbate and could be induced at LL by methyl viologen. We suggest that excess ROS mediate a decrease in the reduced/oxidized glutathione ratio that in turn signals the translational arrest of the rbcL transcript.
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Affiliation(s)
- V Irihimovitch
- Department of Life Sciences, Ben-Gurion University of the Negev, Beer-Sheva 84105, Israel
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135
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Bennett TA, Edwards BS, Sklar LA, Rogelj S. Sulfhydryl regulation of L-selectin shedding: phenylarsine oxide promotes activation-independent L-selectin shedding from leukocytes. JOURNAL OF IMMUNOLOGY (BALTIMORE, MD. : 1950) 2000; 164:4120-9. [PMID: 10754306 DOI: 10.4049/jimmunol.164.8.4120] [Citation(s) in RCA: 88] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
The L-selectin adhesion molecule mediates leukocyte recruitment to inflammatory sites and lymphocyte trafficking through the peripheral lymph nodes. In response to leukocyte activation, L-selectin is proteolytically released from the cell surface, disabling leukocytes from the subsequent L-selectin-dependent interactions. We have found that L-selectin shedding is sensitive to sulfhydryl chemistry; it is promoted by thiol-oxidizing or -blocking reagents and inhibited by reducing reagents. Phenylarsine oxide (PAO), a trivalent arsenical that interacts with vicinal dithiols, is most potent in inducing rapid shedding of L-selectin from isolated neutrophils, eosinophils, and lymphocytes as well as from neutrophils in whole blood. PAO does not cause cell activation, nor does it interfere with integrin function or alter the expression of several other cell surface molecules at the low concentrations that induce L-selectin shedding. PAO is not required to enter the cell to induce L-selectin shedding. TAPI-2 ((N-(D,L-[2-(hydroxyaminocarbonyl)-methyl]-4-methylpentanoyl)-L-3-(tert-butyl)-alanyl-l -alanine, 2-aminoethyl amide), which has previously been shown to inhibit the activation-dependent L-selectin shedding, is also capable of inhibiting PAO-induced L-selectin shedding. We hypothesize that PAO-induced L-selectin shedding involves a regulatory molecule, such as protein disulfide isomerase (PDI), an enzyme that plays a role in the formation and rearrangement of disulfide bonds, contains PAO-binding, vicinal dithiol-active sites, and is expressed on the neutrophil surface. Cell surface expression of PDI, L-selectin shedding induced by PDI-blocking Abs and by bacitracin, a known inhibitor of PDI activity, and direct binding of PDI to PAO, provide supporting evidence for this hypothesis.
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Affiliation(s)
- T A Bennett
- Department of Pathology, Division of Cytometry, Cancer Research Facility, University of New Mexico School of Medicine, Albuquerque, NM 87131, USA
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136
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Grossman AR. Chlamydomonas reinhardtii and photosynthesis: genetics to genomics. CURRENT OPINION IN PLANT BIOLOGY 2000; 3:132-137. [PMID: 10712957 DOI: 10.1016/s1369-5266(99)00053-9] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
Abstract
Genetic and physiological features of the green alga Chlamydomonas reinhardtii have provided a useful model for elucidating the function, biogenesis and regulation of the photosynthetic apparatus. Combining these characteristics with newly developed molecular technologies for engineering Chlamydomonas and the promise of global analyses of nuclear and chloroplast gene expression will add a new perspective to views on photosynthetic function and regulation.
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Affiliation(s)
- A R Grossman
- Department of Plant Biology, The Carnegie Institution of Washington, Stanford 94305, USA.
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137
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Fong CL, Lentz A, Mayfield SP. Disulfide bond formation between RNA binding domains is used to regulate mRNA binding activity of the chloroplast poly(A)-binding protein. J Biol Chem 2000; 275:8275-8. [PMID: 10722654 DOI: 10.1074/jbc.275.12.8275] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Binding of the chloroplast poly(A)-binding protein, RB47, to the psbA mRNA is regulated in response to light and is required for translation of this mRNA in chloroplasts. The RNA binding activity of RB47 can be modulated in vitro by oxidation and reduction. Site-directed mutations to individual cysteine residues in each of the four RNA binding domains of RB47 showed that changing single cysteines to serines in domains 2 or 3 reduced, but did not eliminate, the ability of RB47 to be redox-regulated. Simultaneously changing cysteines to serines in both domains 2 and 3 resulted in the production of RB47 protein that was insensitive to redox regulation but retained the ability to bind the psbA mRNA at high affinity. The poly(A)-binding protein from Saccharomyces cerevisiae lacks cysteine residues in RNA binding domains 2 and 3, and this poly(A)-binding protein lacks the ability to be regulated by oxidation or reduction. These data show that disulfide bond formation between RNA binding domains in a poly(A)-binding protein can be used to regulate the ability of this protein to bind mRNA and suggest that redox regulation of RNA binding activity may be used to regulate translation in organisms whose poly(A)-binding proteins contain these critical cysteine residues.
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Affiliation(s)
- C L Fong
- Department of Cell Biology and the Skaggs Institute for Chemical Biology, The Scripps Research Institute, La Jolla, California 92037, USA
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138
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Staub JM, Garcia B, Graves J, Hajdukiewicz PT, Hunter P, Nehra N, Paradkar V, Schlittler M, Carroll JA, Spatola L, Ward D, Ye G, Russell DA. High-yield production of a human therapeutic protein in tobacco chloroplasts. Nat Biotechnol 2000; 18:333-8. [PMID: 10700152 DOI: 10.1038/73796] [Citation(s) in RCA: 270] [Impact Index Per Article: 11.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Abstract
Transgenic plants have become attractive systems for production of human therapeutic proteins because of the reduced risk of mammalian viral contaminants, the ability to do large scale-up at low cost, and the low maintenance requirements. Here we report a feasibility study for production of a human therapeutic protein through transplastomic transformation technology, which has the additional advantage of increased biological containment by apparent elimination of the transmission of transgenes through pollen. We show that chloroplasts can express a secretory protein, human somatotropin, in a soluble, biologically active, disulfide-bonded form. High concentrations of recombinant protein accumulation are observed (>7% total soluble protein), more than 300-fold higher than a similar gene expressed using a nuclear transgenic approach. The plastid-expressed somatotropin is nearly devoid of complex post-translational modifications, effectively increasing the amount of usable recombinant protein. We also describe approaches to obtain a somatotropin with a non-methionine N terminus, similar to the native human protein. The results indicate that chloroplasts are a highly efficient vehicle for the potential production of pharmaceutical proteins in plants.
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Affiliation(s)
- J M Staub
- Monsanto Company, 700 Chesterfield Village Parkway North, St. Louis, MO 63198, USA.
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139
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Murakami S, Kondo Y, Nakano T, Sato F. Protease activity of CND41, a chloroplast nucleoid DNA-binding protein, isolated from cultured tobacco cells. FEBS Lett 2000; 468:15-8. [PMID: 10683432 DOI: 10.1016/s0014-5793(00)01186-8] [Citation(s) in RCA: 66] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Abstract
CND41 is a 41 kDa DNA-binding protein isolated from chloroplast nucleoids of cultured tobacco cells. The presence of the active domain of aspartic protease in the deduced amino acid sequence of CND41 suggests that it has proteolytic activity. To confirm this, CND41 was highly purified from cultured tobacco cells and its proteolytic activity was characterized with fluorescein isothiocyanate-labeled hemoglobin as the substrate. The purified CND41 had strong proteolytic activity at an acidic pH (pH 2-4). This activity was inhibited by various chemicals, including the nucleoside triphosphates, NADPH, Fe(3+) and sodium dodecyl sulfate.
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Affiliation(s)
- S Murakami
- Department of Applied Life Sciences, Graduate School of Agriculture, Kyoto University, Kyoto, Japan
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140
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Trebitsh T, Levitan A, Sofer A, Danon A. Translation of chloroplast psbA mRNA is modulated in the light by counteracting oxidizing and reducing activities. Mol Cell Biol 2000; 20:1116-23. [PMID: 10648596 PMCID: PMC85229 DOI: 10.1128/mcb.20.4.1116-1123.2000] [Citation(s) in RCA: 102] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Light has been proposed to stimulate the translation of Chlamydomonas reinhardtii chloroplast psbA mRNA by activating a protein complex associated with the 5' untranslated region of this mRNA. The protein complex contains a redox-active regulatory site responsive to thioredoxin. We identified RB60, a protein disulfide isomerase-like member of the protein complex, as carrying the redox-active regulatory site composed of vicinal dithiol. We assayed in parallel the redox state of RB60 and translation of psbA mRNA in intact chloroplasts. Light activated the specific oxidation of RB60, on the one hand, and reduced RB60, probably via the ferredoxin-thioredoxin system, on the other. Higher light intensities increased the pool of reduced RB60 and the rate of psbA mRNA translation, suggesting that a counterbalanced action of reducing and oxidizing activities modulates the translation of psbA mRNA in parallel with fluctuating light intensities. In the dark, chemical reduction of the vicinal dithiol site did not activate translation. These results suggest a mechanism by which light primes redox-regulated translation by an unknown mechanism and then the rate of translation is determined by the reduction-oxidation of a sensor protein located in a complex bound to the 5' untranslated region of the chloroplast mRNA.
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Affiliation(s)
- T Trebitsh
- Department of Plant Sciences, Weizmann Institute of Science, Rehovot 76100, Israel
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141
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Qin J, Yang Y, Velyvis A, Gronenborn A. Molecular views of redox regulation: three-dimensional structures of redox regulatory proteins and protein complexes. Antioxid Redox Signal 2000; 2:827-40. [PMID: 11213487 DOI: 10.1089/ars.2000.2.4-827] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 10/22/2022]
Abstract
The last decade has witnessed the explosion of research on redox-controlled cellular and biochemical processes. Whereas the vast majority of these studies have centered on clinical, genetic, and biochemical aspects of redox signaling and regulation inside and outside the cell, a significant number of nuclear magnetic resonance (NMR) and crystallographic studies have been undertaken to obtain an atomic-level understanding of the mechanisms of the redox regulation. This review highlights the recent progress of three-dimensional structure determination of key proteins and protein complexes involved in redox regulation. An increased list of such class of protein structures and their complexes with ligands will provide invaluable insight into the molecular basis of redox-regulatory processes and may be useful for the future development of therapeutic agents for redox-related diseases.
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Affiliation(s)
- J Qin
- Structural Biology Program, Lerner Research Institute, Cleveland Clinic Foundation, Cleveland, OH 44195, USA.
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142
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Salvador ML, Klein U. The redox state regulates RNA degradation in the chloroplast of Chlamydomonas reinhardtii. PLANT PHYSIOLOGY 1999; 121:1367-74. [PMID: 10594124 PMCID: PMC59504 DOI: 10.1104/pp.121.4.1367] [Citation(s) in RCA: 39] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/18/1999] [Accepted: 09/01/1999] [Indexed: 05/17/2023]
Abstract
A Chlamydomonas reinhardtii chloroplast transformant, designated MU7, carrying a chimeric (rbcL promoter: beta-glucuronidase [GUS]: psaB 3' end) gene whose transcripts have been found previously to be unstable in light (half-life of 20 min in light as opposed to a half-life of 5 h in the dark), was used to study the role of electron transport and of the redox state in the degradation of chloroplast transcripts in the light. Blocking photosynthetic electron transport with 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU) prevented the light-dependent breakdown of the pool of GUS transcripts in MU7 cells. Diamide, an oxidizing agent, caused a measurable delay in the degradation of GUS transcripts in the light. The addition of dithiothreitol (DTT), a dithiol reductant, to MU7 cells in which GUS transcript levels were stabilized by DCMU induced degradation of GUS transcripts. Similarly, DTT induced a decrease in the levels of GUS transcripts when added to MU7 cells in the dark period of the light/dark cycle, a period in which GUS transcript levels normally increase. The levels of transcripts of endogenous chloroplast genes were affected by DCMU and DTT in the same direction as levels of GUS transcripts. The results suggest a regulatory role of the redox state in the degradation of chloroplast transcripts in C. reinhardtii.
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Affiliation(s)
- M L Salvador
- Department of Biochemistry and Molecular Biology, University of Valencia, Doctor Moliner 50, 46100 Valencia, Spain
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143
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Noiva R. Protein disulfide isomerase: the multifunctional redox chaperone of the endoplasmic reticulum. Semin Cell Dev Biol 1999; 10:481-93. [PMID: 10597631 DOI: 10.1006/scdb.1999.0319] [Citation(s) in RCA: 215] [Impact Index Per Article: 8.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
Protein disulfide isomerase (PDI) is a protein-thiol oxidoreductase that catalyzes the oxidation, reduction and isomerization of protein disulfides. In the endoplasmic reticulum PDI catalyzes both the oxidation and isomerization of disulfides on nascent polypeptides. Under the reducing condition of the cytoplasm, endosomes and cell surface. PDI catalyzes the reduction of protein disulfides. At those locations, PDI has been demonstrated to participate in the regulation of reception function, cell-cell interaction, gene expression, and actin filament polymerization. These activities of PDI will be discussed, as well as its activity as a chaperone and subunit of prolyl 4-hydroxylase and microsomal triglyceride transfer protein.
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Affiliation(s)
- R Noiva
- University of South Dakota School of Medicine, Division of Basic Biomedical Sciences, Biochemistry and Molecular Biology Group, Vermillion 57069, USA.
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144
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Bruick RK, Mayfield SP. Light-activated translation of chloroplast mRNAs. TRENDS IN PLANT SCIENCE 1999; 4:190-195. [PMID: 10322559 DOI: 10.1016/s1360-1385(99)01402-8] [Citation(s) in RCA: 50] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
Abstract
The integrated regulation of mRNA stability, processing and translation facilitates the expression of several chloroplast genes, particularly in response to changes in illumination. Nuclear and chloroplast-encoded factors that mediate the expression of specific chloroplast messages have been characterized from green algae and plants. Recent studies suggest that the chloroplast might have recruited eukaryotic proteins, which are usually found in the cytoplasm or the endoplasmic reticulum, to couple the level of photosynthetic activity to gene expression via translational activation. Consequently, elements required for translational initiation of chloroplast messages differ from their prokaryotic ancestors. These results suggest that chloroplast translational regulation is a hybrid between prokaryotic and eukaryotic systems.
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Affiliation(s)
- RK Bruick
- Dept of Cell Biology and The Skaggs Institute for Chemical Biology, The Scripps Research Institute, 10550 North Torrey Pines Road, La Jolla, CA 92037, USA
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145
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The biogenesis and assembly of photosynthetic proteins in thylakoid membranes1. BIOCHIMICA ET BIOPHYSICA ACTA 1999; 1411:21-85. [PMID: 10216153 DOI: 10.1016/s0005-2728(99)00043-2] [Citation(s) in RCA: 153] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
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146
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DiPietrantonio AM, Hsieh T, Wu JM. Activation of caspase 3 in HL-60 cells exposed to hydrogen peroxide. Biochem Biophys Res Commun 1999; 255:477-82. [PMID: 10049734 DOI: 10.1006/bbrc.1999.0208] [Citation(s) in RCA: 83] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Recent studies have suggested that hydrogen peroxide (H2O2), a reactive compound formed endogenously in the breakdown of superoxide, may mediate the induction of apoptosis in various cell types in response to external stimuli. However, the role of H2O2 in the apoptotic pathway has not been clearly established. The purpose of this study was to determine if H2O2 treatment could induce apoptosis through the activation of caspases. Doses of H2O2 ranging from 10 microM to 100 microM, when added to HL-60 cells, resulted in the cleavage of poly(ADP-ribose) polymerase (PARP) from its native 113 Kd form to a processed 89 Kd fragment, indicative of cells undergoing apoptosis. PARP was predominantly in the fragmented form when doses of 20 microM and greater were used. A time course study of changes in PARP processing in H2O2-treated cells revealed that 10 and 50 microM H2O2 required 6 and 3 h, respectively, to specifically degrade PARP, suggesting that the H2O2-induced PARP cleavage is both time and concentration dependent. Since PARP is cleaved by CPP32 (caspase-3), we next determined if H2O2 was capable of effecting changes in CPP32 activity. The caspase activity was assayed using a colorimetric substrate, DEVD-pNa. Results of these experiments showed that H2O2 increased caspase activity at 3 h, corresponding to the time of appearance of fragmented PARP. Also, CPP32 activity and PARP processing were both significantly suppressed by caspase-3 inhibitors. Taken together, these results suggest that H2O2 mediates specific cleavage of PARP and possibly apoptosis by activating caspase 3.
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Affiliation(s)
- A M DiPietrantonio
- Department of Biochemistry and Molecular Biology, New York Medical College, Valhalla 10595, USA
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147
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Abstract
The entire sequence (120-190 kb) of chloroplast genomes has been determined from a dozen plant species. The genome contains from 87 to 183 known genes, of which half encode components involved in translation. These include a complete set of rRNAs and about 30 tRNAs, which are likely to be sufficient to support translation in chloroplasts. RNA editing (mostly C to U base changes) occurs in some chloroplast transcripts, creating start and stop codons and changing codons to retain conserved amino acids. Many components that constitute the chloroplast translational machinery are similar to those of Escherichia coli, whereas only one third of the chloroplast mRNAs contain Shine-Dalgarno-like sequences at the correct positions. Analyses conducted in vivo and in vitro have revealed the existence of multiple mechanisms for translational initiation in chloroplasts.
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Affiliation(s)
- M Sugiura
- Center for Gene Research, Nagoya University, Japan.
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148
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Markus M, Benezra R. Two isoforms of protein disulfide isomerase alter the dimerization status of E2A proteins by a redox mechanism. J Biol Chem 1999; 274:1040-9. [PMID: 9873049 DOI: 10.1074/jbc.274.2.1040] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
We have shown previously that E2A helix-loop-helix proteins spontaneously form an intermolecular disulfide cross-link that is required for stable homodimer binding to DNA (Benezra, R. (1994) Cell 79, 1057-1067). These homodimers are important for the development of B lymphocytes but are not present in other cell lineages. We have purified two proteins that are capable of regulating the formation of this disulfide bond and found them to be members of the protein disulfide isomerase (PDI) family. By regulating the formation of the disulfide cross-link, these proteins are capable of regulating the dimerization state of E proteins. PDI-mediated reduction appears to dissociate E protein homodimers and favors heterodimer formation with other basic helix-loop-helix proteins in both a purified protein system and in cellular extracts. These studies suggest that PDI may play an important role in the regulation of E2A transcription factor dimerization and the development of the B lymphocyte lineage.
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Affiliation(s)
- M Markus
- Cell Biology Program, Memorial Sloan-Kettering Cancer Center, New York, New York 10021, USA
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149
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Bruick RK, Mayfield SP. Processing of the psbA 5' untranslated region in Chlamydomonas reinhardtii depends upon factors mediating ribosome association. J Cell Biol 1998; 143:1145-53. [PMID: 9832545 PMCID: PMC2133069 DOI: 10.1083/jcb.143.5.1145] [Citation(s) in RCA: 47] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/10/1998] [Revised: 10/21/1998] [Indexed: 11/22/2022] Open
Abstract
The 5' untranslated region of the chloroplast psbA mRNA, encoding the D1 protein, is processed in Chlamydomonas reinhardtii. Processing occurs just upstream of a consensus Shine-Dalgarno sequence and results in the removal of 54 nucleotides from the 5' terminus, including a stem-loop element identified previously as an important structure for D1 expression. Examination of this processing event in C. reinhardtii strains containing mutations within the chloroplast or nuclear genomes that block psbA translation reveals a correlation between processing and ribosome association. Mutations within the 5' untranslated region of the psbA mRNA that disrupt the Shine-Dalgarno sequence, acting as a ribosome binding site, preclude translation and prevent mRNA processing. Similarly, nuclear mutations that specifically affect synthesis of the D1 protein specifically affect processing of the psbA mRNA. In vitro, loss of the stem-loop element does not prohibit the binding of a message-specific protein complex required for translational activation of psbA upon illumination. These results are consistent with a hierarchical maturation pathway for chloroplast messages, mediated by nuclear-encoded factors, that integrates mRNA processing, message stability, ribosome association, and translation.
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MESH Headings
- 5' Untranslated Regions/genetics
- 5' Untranslated Regions/metabolism
- Animals
- Base Sequence
- Binding Sites/genetics
- Cell Nucleus/genetics
- Cell Nucleus/metabolism
- Chlamydomonas reinhardtii/genetics
- Chlamydomonas reinhardtii/metabolism
- Chlamydomonas reinhardtii/radiation effects
- Chloroplasts/genetics
- Chloroplasts/metabolism
- DNA Primers/genetics
- Light
- Molecular Sequence Data
- Mutation
- Nucleic Acid Conformation
- Photosynthetic Reaction Center Complex Proteins/genetics
- Photosynthetic Reaction Center Complex Proteins/metabolism
- Photosynthetic Reaction Center Complex Proteins/radiation effects
- Photosystem II Protein Complex
- RNA Processing, Post-Transcriptional
- RNA, Messenger/chemistry
- RNA, Messenger/genetics
- RNA, Messenger/metabolism
- RNA, Plant/chemistry
- RNA, Plant/genetics
- RNA, Plant/metabolism
- RNA, Protozoan/chemistry
- RNA, Protozoan/genetics
- RNA, Protozoan/metabolism
- Ribosomes/metabolism
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Affiliation(s)
- R K Bruick
- Department of Cell Biology and The Skaggs Institute for Chemical Biology, The Scripps Research Institute, La Jolla, California 92037, USA
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150
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Schwarz R, Grossman AR. A response regulator of cyanobacteria integrates diverse environmental signals and is critical for survival under extreme conditions. Proc Natl Acad Sci U S A 1998; 95:11008-13. [PMID: 9724820 PMCID: PMC28011 DOI: 10.1073/pnas.95.18.11008] [Citation(s) in RCA: 105] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/20/1998] [Accepted: 07/06/1998] [Indexed: 11/18/2022] Open
Abstract
Microorganisms must sense their environment and rapidly tune their metabolism to ambient conditions to efficiently use available resources. We have identified a gene encoding a response regulator, NblR, that complements a cyanobacterial mutant unable to degrade its light-harvesting complex (phycobilisome), in response to nutrient deprivation. Cells of the nblR mutant (i) have more phycobilisomes than wild-type cells during nutrient-replete growth, (ii) do not degrade phycobilisomes during sulfur, nitrogen, or phosphorus limitation, (iii) cannot properly modulate the phycobilisome level during exposure to high light, and (iv) die rapidly when starved for either sulfur or nitrogen, or when exposed to high light. Apart from regulation of phycobilisome degradation, NblR modulates additional functions critical for cell survival during nutrient-limited and high-light conditions. NblR does not appear to be involved in acclimation responses that occur only during a specific nutrient limitation. In contrast, it controls at least some of the general acclimation responses; those that occur during any of a number of different stress conditions. NblR plays a pivotal role in integrating different environmental signals that link the metabolism of the cell to light harvesting capabilities and the activities of the photosynthetic apparatus; this modulation is critical for cell survival.
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Affiliation(s)
- R Schwarz
- Department of Plant Biology, The Carnegie Institution of Washington, 260 Panama Street, Stanford, CA 94305, USA
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