The development, inheritance, and origin of the plastid in Euglena

Extremely large and slowly processed precursors to the Euglena light-harvesting chlorophyll a/b binding proteins of photosystem II

Antibody to the Euglena light-harvesting chlorophyll a/b binding protein of photosystem II (LHCPII) immunoprecipitated 207-, 161-, 122-, and 110-kDa proteins from total Euglena proteins pulse-labeled for 10 min with [(35)S]sulfate. The 25.6- and 27.2-kDa LHCPII were barely detectable in the immunoprecipitate. During a 40-min chase with unlabeled sulfate, the amount of radioactivity in the high molecular mass proteins decreased, and the amount of radioactivity in the 25.6- and 27.2-kDa LHCPII increased with kinetics consistent with a precursor-product relationship. The half-life of the high molecular mass proteins was approximately 20 min. The major proteins immunoprecipitated from a nuclease-treated rabbit reticulocyte cell-free translation system programmed with Euglena whole cell or poly(A)(+) RNA had molecular masses corresponding to the molecular masses of the proteins immunoprecipitated from the pulse-labeled in vivo translation products. RNAs of 6.6 and 8.3 kilobases were the only Euglena whole cell and poly(A)(+) RNAs that hybridized to a 0.7-kilobase EcoRI-BamHI fragment of plasmid pAB165, which contains a portion of the coding sequence for Arabidopsis LHCPII. RNAs of this size are more than sufficient to code for proteins of 207 kDa. Taken together, these findings demonstrate that the LHCPIIs of Euglena are initially synthesized as slowly processed precursors with molecular masses of 207, 161, 122, and 110 kDa.

Pathways of assimilatory sulphate reduction in plants and microorganisms

Assimilatory sulphate reduction, largely restricted to plants and microorganisms where it provides reduced sulphur for the formation of amino acids and proteins, nucleic acids, and various sulphur-containing coenzymes, begins with the activation of sulphate through reaction with ATP to form adenosine 5'-phosphosulphate (APS) and adenosine 3'-phosphate 5'-phosphosulphate (PAPS). Two pathways of assimilatory sulphate reduction are known. One, found in some blue-green algae (cyanobacteria) and in all oxygen-envolving eukaryotes, begins with APS where the sulpho group is transferred via APS sulphotransferase to a thiol acceptor (glutathione (G-S-) in Chlorella) to form the organic thiosulphate (G-S-SO-3). The organic thiosulphate appears to be reduced further by an organic thiosulphate reductase employing reduced ferredoxin to form G-S-S-. The terminal sulphur is then thought to be reductively transferred to O-acetylserine via O-acetylserine sulphydrase to form cysteine. A second pathway, found in bacteria and fungi, begins with PAPS where the sulpho group is transferred via PAPS sulphotransferase to an acceptor thiol to form an organic thiosulphate. Since thioredoxin is indispensable, this molecule may be the carrier or may serve to reduce the carrier. NADPH via thioredoxin reductase or glutathione and glutathione reductase reduces thioredoxin. These reactions release sulphite which is further reduced to sulphide by sulphite reductase, employing NADPH. Sulphide is then thought to react with O-acetylserine to form cysteine via O-acetylserine sulphydrase. The cellular location and evolution of these pathways is discussed.

Evolution of the control of pigment and plastid development in photosynthetic organisms

How do bioenergetic organelles relate to the cells they are in and how was this relationship established over the course of evolution? Plastids and mitochondria are viewed as prokaryotic residents in eukaryotic cells. These organelles are semiautonomous: they perpetuate themselves by division but regulate and are subject to regulation by the cell in which they are residents. Although these organelles are usually constitutive, their development is arrested in certain organisms when an inducing substrate is absent (light, for example, in the case of the chloroplast) with the formation of precursor organelles such as proplastids. Various trends in the evolution of photo-control systems are discussed including those concerned with photoperception and photomorphogenesis. The photocontrol of chloroplast development by blue and red light is discussed in relation to its possible evolutionary origins in a system for finding the right light for photosynthesis. Models for various types of cellular regulation by light during chloroplast development are discussed. Also considered is the evolution of plastid pigments in response to available light. A parallel evolution of accessory pigments and chlorophylls is suggested which led to chlorophyll reaction centers serving as energy sinks for light absorbed by accessory pigments and, therefore, having their absorptions pushed to the longest possible wavelengths as accessory pigments evolved to fill the middle of the spectrum in response to ecological selection. An endosymbiotic origin of bioenergetic organelles is suggested based on polyphyletic origins of chloroplasts from a number of oxygenic procaryotic precursors. The similarity between proplastids and these oxygenic procaryotes suggests that the original invading organelle may have resembled a modern proplastid rather than a mature chloroplast.

Messenger RNA of the large subunit of ribulose-1,5-bisphosphate carboxylase from Chlamydomonas reinhardi. Isolation and properties

Polysomes specifically synthesizing the large subunit of ribulose-1,5-bisphosphate carboxylase were isolated from Chlamydomonas reinhardi cells by the indirect immunoprecipitation method. Electrophoretic analysis showed that the immunoprecipitated polysomes were of chloroplast origin. The mRNA coding for the large subunit which was purified from immunoprecipitated polysomes migrated at the 19-S position on sucrose density gradients, and its molecular weight was estimated to be 7.3 x 10(5) by acid-urea/agarose gel electrophoresis. The mRNA was translated in vivo with a cell-free protein-synthesizing system derived from Escherichia coli to give full-length large-subunit polypeptides.

Comments on the translational and transcriptional origin of Euglena chloroplastic aminoacyl-tRNA synthetases

A response to: "A consideration of Euglena gracilis W3BUL as a cytoplasmic control for the wild-type phenylalanyl-tRNA synthetase system" and "A reinvestigation of the sites of transcription and translation of Euglena chloroplastic phenylalanyl-tRNA synthetase" by J. L. Lesiewicz and D. S. Herson.

Chloroplast and cytoplasmic ribosomes of Euglena: selective binding of dihydrostreptomycin to chloroplast ribosomes

Dihydrostreptomycin binds preferentially to chloroplast ribosomes of wild-type Euglena gracilis Klebs var. bacillaris Pringsheim. The K(diss) for the wild-type chloroplast ribosome-dihydrostreptomycin complex is 2 x 10(-7) M, a value comparable with that found for the Escherichia coli ribosome-dihydrostreptomycin complex. Chloroplast ribosomes isolated from the streptomycin-resistant mutant Sm(1) (r)BNgL and cytoplasmic ribosomes from wild-type have a much lower affinity for the antibiotic. The K(diss) for the chloroplast ribosome-dihydrostreptomycin complex of Sm(1) (r) is 387 x 10(-7) M, and the value for the cytoplasmic ribosome-dihydrostreptomycin complex of the wild type is 1,400 x 10(-7) M. Streptomycin competes with dihydrostreptomycin for the chloroplast ribosome binding site, and preincubation of streptomycin with hydroxylamine prevents the binding of streptomycin to the chloroplast ribosome. These results indicate that the inhibition of chloroplast development and replication in Euglena by streptomycin and dihydrostreptomycin is related to the specific inhibition of protein synthesis on the chloroplast ribosomes of Euglena.

The sites of transcription and translation for Euglena chloroplastic aminoacyl-tRNA synthetases

We find that cycloheximide completely blocks the light-induced apearance of Euglena chloroplastic aminoacyl-tRNA synthetases in dark-grown cells of Euglena gracilis var. bacillaris. Streptomycin, on the other hand, has no effect on the light-induction of these organellar enzymes. These observations, together with the finding that an aplastidic mutant (strain W(3)BUL, which has neither significant plastid structure nor detectable chloroplast DNA) contains low levels of the chloroplastic synthetases, indicate that the chloroplastic synthetases are transcriptional products of nuclear genes and are translated on cytoplasmic ribosomes prior to compartmentalization within the chloroplasts.