The localization of translation can direct the polypeptide product to the proper intracellular compartment. Our results reveal translation by cytosolic ribosomes on a domain of the chloroplast envelope in the unicellular green alga Chlamydomonas (Chlamydomonas reinhardtii). We show that this envelope domain of isolated chloroplasts retains translationally active ribosomes and mRNAs encoding chloroplast proteins.
View Article and Find Full Text PDFCytoplasmic RNA granules compartmentalize phases of the translation cycle in eukaryotes. We previously reported the localization of oxidized RNA to cytoplasmic foci called oxidized RNA bodies (ORBs) in human cells. We show here that ORBs are RNA granules in Saccharomyces cerevisiae.
View Article and Find Full Text PDFIn order to better understand the environmental risks of the rare earth elements (REEs), it is necessary to determine their fate and biological effects under environmentally relevant conditions (e.g. at low concentrations, REE mixtures).
View Article and Find Full Text PDFIntracellular processes can be localized for efficiency or regulation. For example, localized mRNA translation by chloroplastic ribosomes occurs in the biogenesis of PSII, one of the two photosystems of the photosynthetic electron transport chain in the chloroplasts of plants and algae. The biogenesis of PSI and PSII requires the synthesis and assembly of their constituent polypeptide subunits, pigments, and cofactors.
View Article and Find Full Text PDFOrganelles are intracellular compartments which are themselves compartmentalized. Biogenic and metabolic processes are localized to specialized domains or microcompartments to enhance their efficiency and suppress deleterious side reactions. An example of intra-organellar compartmentalization is the pyrenoid in the chloroplasts of algae and hornworts.
View Article and Find Full Text PDFPhotosystem II is the first of two light-driven oxidoreductase complexes in oxygenic photosynthesis. The biogenesis of photosystem II requires the synthesis of polypeptide subunits encoded by the genomes in the chloroplast and the nucleus. In the chloroplast of the green alga Chlamydomonas reinhardtii, the synthesis of each subunit requires interactions between the 5' UTR of the mRNA encoding it and gene-specific translation factors.
View Article and Find Full Text PDFThe oxidation of biological molecules by reactive oxygen species (ROS) can render them inactive or toxic. This includes the oxidation of RNA, which appears to underlie the detrimental effects of oxidative stress, aging and certain neurodegenerative diseases. Here, we investigate the management of oxidized RNA in the chloroplast of the green alga Chlamydomonas reinhardtii.
View Article and Find Full Text PDFBiochim Biophys Acta
September 2015
Chloroplast genomes encode 100-200 proteins which function in photosynthesis, the organellar genetic system, and other pathways and processes. These proteins are synthesized by a complete translation system within the chloroplast, with bacterial-type ribosomes and translation factors. Here, we review translational regulation in chloroplasts, focusing on changes in translation rates which occur in response to requirements for proteins encoded by the chloroplast genome for development and homeostasis.
View Article and Find Full Text PDFThe widespread use of nanoparticles (NPs) raises concern over their potential toxicological effects in humans and ecosystems. Here we used transcriptome sequencing (RNA-seq) to evaluate the effects of exposure to four different metal-based NPs, nano-Ag (nAg), nano-TiO2 (nTiO2), nano-ZnO (nZnO), and CdTe/CdS quantum dots (QDs), in the eukaryotic green alga Chlamydomonas reinhardtii. The transcriptome was characterized before and after exposure to each NP type.
View Article and Find Full Text PDFBiochim Biophys Acta
February 2013
Cells have complex membranous organelles for the compartmentalization and the regulation of most intracellular processes. Organelle biogenesis and maintenance requires newly synthesized proteins, each of which needs to go from the ribosome translating its mRNA to the correct membrane for insertion or transclocation to an a organellar subcompartment. Decades of research have revealed how proteins are targeted to the correct organelle and translocated across one or more organelle membranes ro the compartment where they function.
View Article and Find Full Text PDFMetabolic control of gene expression coordinates the levels of specific gene products to meet cellular demand for their activities. This control can be exerted by metabolites acting as regulatory signals and/or a class of metabolic enzymes with dual functions as regulators of gene expression. However, little is known about how metabolic signals affect the balance between enzymatic and regulatory roles of these dual functional proteins.
View Article and Find Full Text PDFProc Natl Acad Sci U S A
November 2012
The polypeptide subunits of the photosynthetic electron transport complexes in plants and algae are encoded by two genomes. Nuclear genome-encoded subunits are synthesized in the cytoplasm by 80S ribosomes, imported across the chloroplast envelope, and assembled with the subunits that are encoded by the plastid genome. Plastid genome-encoded subunits are synthesized by 70S chloroplast ribosomes directly into membranes that are widely believed to belong to the photosynthetic thylakoid vesicles.
View Article and Find Full Text PDFHere we describe how to use fluorescence in situ hybridization and immunofluorescence staining to determine the in situ distributions of specific mRNAs and proteins in Chlamydomonas reinhardtii. This unicellular eukaryotic green alga is a major model organism in cell biological research. Chlamydomonas is well suited for these approaches because one can determine the cytological location of fluorescence signals within a characteristic cellular anatomy relative to prominent cytological markers.
View Article and Find Full Text PDFProc Natl Acad Sci U S A
February 2009
The compartmentalization of eukaryotic cells requires that newly synthesized proteins be targeted to the compartments in which they function. In chloroplasts, a few thousand proteins function in photosynthesis, expression of the chloroplast genome, and other processes. Most chloroplast proteins are synthesized in the cytoplasm, imported, and then targeted to a specific chloroplast compartment.
View Article and Find Full Text PDFEukaryotic cells under stress repress translation and localize these messenger RNAs (mRNAs) to cytoplasmic RNA granules. We show that specific stress stimuli induce the assembly of RNA granules in an organelle with bacterial ancestry, the chloroplast of Chlamydomonas reinhardtii. These chloroplast stress granules (cpSGs) form during oxidative stress and disassemble during recovery from stress.
View Article and Find Full Text PDFIn the natural environment, cadmium is often found as a trace contaminant. Due to the complexity of Cd speciation and the heterogeneity of natural systems and processes, it is often difficult to determine clear relationships between analytical measurements of Cd and its induced biological response. Measurements of gene induction can be used to identify molecular mechanisms underlying toxicity and to quantify sublethal responses to trace contaminants.
View Article and Find Full Text PDFMany proteins of the photosynthesis complexes are encoded by the genome of the chloroplast and synthesized by bacterium-like ribosomes within this organelle. To determine where proteins are synthesized for the de novo assembly and repair of photosystem II (PSII) in the chloroplast of Chlamydomonas reinhardtii, we used fluorescence in situ hybridization, immunofluorescence staining, and confocal microscopy. These locations were defined as having colocalized chloroplast mRNAs encoding PSII subunits and proteins of the chloroplast translation machinery specifically under conditions of PSII subunit synthesis.
View Article and Find Full Text PDFTranslation of the chloroplast psbC mRNA in the unicellular eukaryotic alga Chlamydomonas reinhardtii is controlled by interactions between its 547-base 5' untranslated region and the products of the nuclear loci TBC1, TBC2, and possibly TBC3. In this study, a series of site-directed mutations in this region was generated and the ability of these constructs to drive expression of a reporter gene was assayed in chloroplast transformants that are wild type or mutant at these nuclear loci. Two regions located in the middle of the 5' leader and near the initiation codon are important for translation.
View Article and Find Full Text PDFSeveral membrane proteins were previously shown to bind to the 5' leader of the chloroplast psbC mRNA in the unicellular eukaryotic alga Chlamydomonas reinhardtii. This study showed that these proteins have affinity for AU-rich RNAs, as determined by competition experiments. In addition, their binding activities are enhanced 13-15-fold by light, and a 46 kDa protein is activated within 1-10 min.
View Article and Find Full Text PDFGenetic 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.
View Article and Find Full Text PDFThe evolution of eukaryotes was punctuated by invasions of the bacteria that have evolved to mitochondria and plastids. These bacterial endosymbionts founded major eukaryotic lineages by enabling them to carry out aerobic respiration and oxygenic photosynthesis. Yet, having evolved as free-living organisms, they were at first poorly adapted organelles.
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