Location of the single gene for elongation factor Tu on the Euglena gracilis chloroplast chromosome

Photo and Nutritional Regulation of Euglena Organelle Development

Euglena can use light and CO₂, photosynthesis, as well as a large variety of organic molecules as the sole source of carbon and energy for growth. Light induces the enzymes, in this case an entire organelle, the chloroplast, that is required to use CO₂ as the sole source of carbon and energy for growth. Ethanol, but not malate, inhibits the photoinduction of chloroplast enzymes and induces the synthesis of the glyoxylate cycle enzymes that comprise the unique metabolic pathway leading to two carbon, ethanol and acetate, assimilation. In resting, carbon starved cells, light mobilizes the degradation of the storage carbohydrate paramylum and transiently induces the mitochondrial proteins required for the aerobic metabolism of paramylum to provide the carbon and energy required for chloroplast development. Other mitochondrial proteins are degraded upon light exposure providing the amino acids required for the synthesis of light induced proteins. Changes in protein levels are due to increased and decreased rates of synthesis rather than changes in degradation rates. Changes in protein synthesis rates occur in the absence of a concomitant increase in the levels of mRNAs encoding these proteins indicative of photo and metabolic control at the translational rather than the transcriptional level. The fraction of mRNA encoding a light induced protein such as the light harvesting chlorophyll a/b binding protein of photosystem II, (LHCPII) associated with polysomes in the dark is similar to the fraction associated with polysomes in the light indicative of photoregulation at the level of translational elongation. Ethanol, a carbon source whose assimilation requires carbon source specific enzymes, the glyoxylate cycle enzymes, represses the synthesis of chloroplast enzymes uniquely required to use light and CO₂ as the sole source of carbon and energy for growth. The catabolite sensitivity of chloroplast development provides a mechanism to prioritize carbon source utilization. Euglena uses all of its resources to develop the metabolic capacity to utilize carbon sources such as ethanol which are rarely in the environment and delays until the rare carbon source is no longer available forming the chloroplast which is required to utilize the ubiquitous carbon source, light and CO₂.

The localization and orientation of specific genes in the chloroplast chromosome of Vicia faba

The genes for six chloroplast polypeptides have been localized on the map of Vicia faba chloroplast DNA using heterologous probes. These include the three subunits (α, β, ε) of CF1 of ATP synthase, subunit III of CF0 from ATP synthase, the 32 kilodalton thylakoidal membrane protein of photosystem II and cytochrome f of the electron transport chain. The direction of transcription has been determined for the three subunits of CF1 and the 32 kilodalton thylakoidal protein. The physical map of the chloroplast DNA has also been expanded to include Sma1 sites in addition to previously mapped restriction enzyme sites. Finally, the genetic arrangement of Vicia faba chloroplast DNA was compared to other known genetic maps.

Genes for the plastid elongation factor Tu and ribosomal protein S7 and six tRNA genes on the 73 kb DNA from Astasia longa that resembles the chloroplast DNA of Euglena

The nucleotide sequence of a 6156 bp segment of the circular 73 kb DNA from Astasia longa resembling the chloroplast DNA of Euglena was determined. The genes for the plastid elongation factor Tu (tufA) and the ribosomal protein S7 (rps7), six tRNA genes (trnQ, trnS, trnG, trnM, trnT, trnR), and three open reading frames were identified. These genes show a high degree of sequence similarity (73%-99%) to the corresponding genes on the Euglena chloroplast genome. The tufA gene contains two small AT-rich introns within its coding region. Northern analysis revealed the in vivo transcription of the tufA gene and of a reading frame of 456 codons into monocistronic mRNAs of 1.3 and 1.4 kb, respectively. The arrangement and organization of the genes on the 73 kb DNA of the colourless heterotrophic flagellate Astasia and the chloroplast DNA of autotrophic Euglena are compared.

The two genes for the P700 chlorophyll a apoproteins on the Euglena gracilis chloroplast genome contain multiple introns

We have determined the complete nucleotide sequence of the two genes encoding the P700 chlorophyll a apoproteins of the photosystem I reaction center of the Euglena gracilis chloroplast genome. The two genes are separated by 77 bp, are of the same polarity, and span a region which is greater than 9.0 kbp. The psaA gene (751 codons) is interrupted by three introns and the psaB gene (734 codons) by six introns. The introns range in size from 361 to 590 bp, whereas the exons range in size from 42 to 1,194 bp. The introns are extremely AT rich with a pronounced base bias of T greater than A greater than G greater than C in the RNA-like strand. Like other interrupted protein genes in the Euglena chloroplast genome, the psaA and psaB introns are similar to mitochondrial group II introns in having the splice junction consensus sequence, 5' GTGCGNTTCG ..... INTRON ..... TTAATTTTAT 3' and conserved secondary structural features. Except for the placement of the first intron, the intron-exon organization of these two highly homologous genes is not conserved. The other introns fall at or near putative surface domains of the predicted gene products. The psaA and psaB gene products are 74% homologous to one another and 93% and 95% homologous, respectively, to the psaA and psaB gene products of higher plant chloroplasts. The predicted secondary structure derived from the primary amino acid sequence has 11 potential membrane-spanning domains.

Location, nucleotide sequence and expression of the proton-translocating subunit gene of theE. gracilis chloroplast ATP synthase

A 1700 base pairHindIII restriction fragment from theE. gracilis chloroplast chromosome has been shown to contain the gene for the proton-translocating subunit of the ATP synthase (atpH). The gene was mapped by heterologous hybridization using internal sequences of the gene from wheat and spinach chloroplast DNA. Each chloroplast chromosome contains a single copy of atpH, which is located close to the gene for the alpha subunit of the ATP synthase (atpA). The nucleotide sequence of the gene is uninterrupted by introns. The predicted sequence of 77 amino acids is 70% homologous to that of the wheat and spinach polypeptides. The gene is expressedin vivo as shown by hybridization of atpH probes to cellulose nitrate filter blots of total chloroplast RNA. 5'-proximal to the atpH locus on the clonedHindIII fragment are 38 codons from the carboxy terminus of an open reading frame which may be another ATP synthase subunit. Transcription of the ORF and the atpH gene may be as part of a large polycistronic mRNA.

Localization and nucleotide sequences of the tRNA GCC (Gly) , tRNA GUC (Asp) and tRNA GCA (Cys) genes from wheat chloroplast

The location on the wheat chloroplast DNA map and the nucleotide sequences of the genes coding for tRNA GCC (Gly) (trnG-GCC), tRNA GUC (Asp) (trnD-GUC) and tRNA GCA (Cys) (trnC-GCA) have been determined. These three genes are located in the large single copy region of the chloroplast genome, about half-way between one of the inverted repeats and the gene for the α subunit of ATP synthase. They are located on two Bam H1 fragments, called B6 and B18 by Bowmanet al. (1), which are separated by about 450 bp and which were cloned in our laboratory to allow sequencing. ThetrnD-GUC andtrnC-GCA sequences show 98.6 and 89% homology, respectively, with the corresponding spinach chloroplast tRNA genes sequences (2), which are the only other higher plant chloroplasttrnD-GUC andtrnC-GCA sequenced so far, while no othertrnG-GCC sequence has been published. ThetrnG-GCC sequence shows only 58% homology with the corresponding gene sequence inEuglena chloroplasts (3).

The gene encoding translation initiation factor 3 is highly conserved in gram-negative bacteria

A 1.1-kb Hp alpha I fragment of the Escherichia coli chromosome containing the gene for translation initiation factor 3 was employed as a probe in heterologous hybridization to chromosomal DNA from a variety of other procaryotes. Positive hybridization was observed to DNA derived from all gram-negative bacteria tested. In contrast, no hybridization to DNA from gram-positive bacteria was detected. In addition, homologous sequences were found in Euglena gracilis chloroplast DNA, while this was not the case with Saccharomyces cerevisiae mitochondrial DNA. These results are discussed in light of existing data on the components and mechanism of translation initiation in the various organisms and organelles employed in this study.

Selective in vitro transcription of chloroplast genes

Transcription of Euglena gracilis chloroplast genes has been investigated by using in vitro transcription systems. A DNA-dependent RNA polymerase responsible for the transcription of rRNA genes has been isolated as a nucleoprotein complex (transcriptionally active chromosome). The RNA polymerase remains tightly bound to the chloroplast DNA template and does not initiate transcription with cloned chloroplast genes. A transcriptionally active extract has been prepared from intact Euglena chloroplasts. The soluble RNA polymerase in this extract recognizes cloned chloroplast tRNA genes and tRNA-sized products have been detected after transcription. The tRNA-sized molecules specifically hybridize to the tRNA genes in the plasmid DNA. At least five tRNA-sized products have been identified from transcription of a trnY1trnH1-trnM1-trnE1-trnW1-trnG1 cluster. Evidence is also presented that processing enzymes in the chloroplast-extract can recognize a polycistronic tRNAVal-tRNAAsn-tRNAArg precursor and process it into tRNA-sized molecules. Truncated templates have been used to demonstrate that the chloroplast tRNA genes are actively transcribed. From a comparison of 5' flanking sequences in chloroplast tRNA genes, a consensus sequence which might function as a promoter, has been identified. The properties of the RNA polymerase involved in the transcription of chloroplast rRNA genes and tRNA genes have been investigated and compared.