[The gap1 operon of the cyanobacterium Synechococcus PCC 7942 carries a gene encoding glycogen phosphorylase and is induced under anaerobic conditions]. / GAP1-operon tsianobakterii Synechococcus PCC 7942 kodiruet glikogenfosforilazu i indutsiruetsia v anaéusloviiakh.

The cloning and sequencing of the gap1 operon, which encodes the glycolytic NAD-specific glyceraldehyde-3-phosphate dehydrogenase in the cyanobacterium Synechococcus PCC 7942, showed that the gap1 gene is closely linked to the glgP gene encoding glycogen phosphorylase (an enzyme that catalyzes the first step of glycogen degradation). Northern blotting experiments showed that the gap1 and glgP genes are co-expressed and organized in a bicistronic operon, whose expression is enhanced under anaerobic conditions. The nucleotide sequence of the operon has been submitted to GenBank under accession number AF428099.

[The gap3 gene of Synechococcus PCC 7942 is induced during adaptation to low CO2 concentrations]. / GAP3-gen tsianobakterii Synechococcus PCC 7942 ékspressiruetsia v usloviiakh adaptatsii k nizkim kontsentratsiiam CO2.

The gap3 genes of the Synechococcus and Anabaena cyanobacteria fulfill so far unknown function. A homolog of this gene has recently been found in the nuclear genomes of diplonemids, which are heterotrophic flagellates closely related to kinetoplastids and euglenoids. To understand the function of the gap3 gene in the cyanobacteria, we performed Northern blotting experiments with the gap3 probes under different growth conditions. Under the standard photosynthetic growth conditions (high illumination and 1% CO2 in the gas phase), the expression of the gap3 gene was very low, but significantly increased during cell adaptation to the low CO2 concentration (0.03%). The gap3 operon was expressed as a polycistronic transcript of about 7 kb in size, which included ORF2 (1259 bp) immediately downstream of gap3. ORF2 probably encodes a putative transporter of HCO3. The nucleotide sequence of ORF2 has been submitted to GenBank under accession number AF 428100.

[On the involvement of the regulatory gene prqR in the development of resistance to methyl viologen in cyanobacterium Synechocystis sp. PCC6803]. / Ob uchastii reguliartornogo gena prqR v razvitii ustoichivosti k metilviologenu u tsianobakterii Synechocystis sp. PCC6803.

The role of the prqR gene in the regulation of the adaptive response of the cyanobacterium Synechocystis sp. PCC6803 to the oxidative stress induced with methyl viologen (MV) was studied. For this, transcription activity of prqR and the genes, which may be involved in the control of resistance to MV, was determined by means of Northern blot hybridization in wild-type cells and in the MV-resistant Prq20 mutant with a mutation located in the DNA-binding domain of the PrqR protein. It was ascertained that the prqR gene is a component of the prqR-prqA operon and down regulates its transcription. In cells of the wild-type strain containing MV, the autorepressor activity of the PrqR protein enhances and transcription of mvrA and sodB genes encoding an respectively assumed transporter protein and iron-containing superoxide dismutase increases. The prqR gene may be involved in the negative, indirect control of transcription of these genes. The Prq20 mutant is characterized by an MV-independent derepression of the prqR-prqA operon and by a slightly increased transcription of mvrA and sodB genes not stimulated by MV. Nevertheless, the expression of mvrA and sodB genes was lower than in wild-type cells after the MV treatment. On the strength of this evidence, it is assumed that the main mechanism underlying for the resistance to MV in the Prq20 mutant is derepression of the prqA gene, the product of which is homologous to multidrug transporters, drug efflux proteins.

The TATA box and a Myb binding site are essential for anaerobic expression of a maize GapC4 minimal promoter in tobacco.

The maize GapC4 promoter harbours a complex arrangement of cis-sequences involved in activation of anaerobic gene expression in tobacco. As shown by transient expression assays, four copies of a 50 bp anaerobic response element (ARE) increase anaerobic gene expression compared to the ARE alone. Expression strength is similar to a 190 bp fragment that contains most sequences required for anaerobic expression, including the 50 bp ARE. This supports the notion that redundancy of cis-acting sequences contribute to the anaerobic expression strength of the promoter. Mutation analysis of the 50 bp ARE revealed that cis-regulatory sequences are located within 30 bp at the 5' end of the ARE. Of these 30 bp a putative binding site for a Myb transcription factor is essential for anaerobic induction. The TATA box of the GapC4 promoter is also required for anaerobic gene expression and is bound specifically by a recombinant TATA box binding protein (TBP) from tobacco. A model for anaerobic induction of the GapC4 minimal promoter in tobacco that summarizes the presented data is discussed.

GAPDH gene diversity in spirochetes: a paradigm for genetic promiscuity.

In this study we have determined gap sequences from nine different spirochetes. Phylogenetic analyses of these sequences in the context of all other available eubacterial and a selection of eukaryotic Gap sequences demonstrated that the eubacterial glyceraldehyde-3-phosphate dehydrogenase (GAPDH) gene diversity encompasses at least five highly distinct gene families. Within these gene families, spirochetes show an extreme degree of sequence divergence that is probably the result of several lateral gene transfer events between spirochetes and other eubacterial phyla, and early gene duplications in the eubacterial ancestor. A Gap1 sequence from the syphilis spirochete Treponema pallidum has recently been shown to be closely related to GapC sequences from Euglenozoa. Here we demonstrate that several other spirochetal species are part of this cluster, supporting the conclusion that an interkingdom gene transfer from spirochetes to Euglenozoa must have occurred. Furthermore, we provide evidence that the GAPDH genes present in the protists Parabasalia may also be of spirochetal descent.

Characterization and analysis of an NAD(P)H dehydrogenase transcriptional regulator critical for the survival of cyanobacteria facing inorganic carbon starvation and osmotic stress.

The three Synechocystis PCC6803 genes homologous to proteobacterial Calvin cycle regulators (cbbR) have been analysed. sll0998 appeared to be crucial to cell viability, whereas both sll0030 and sll1594 were found to be dispensable for cell growth. In spite of their sequence homology, Sll0030 and Sll1594 did not appear to regulate the transcription of Calvin cycle key genes. Further analysis of Sll1594 showed that this protein plays an important role in the adaptation to inorganic carbon starvation and osmotic stress. Sll1594 mediates the response to these stress conditions by regulating the transcription of a new regulon including the monocistronic genes sll1594 and slr1727 (encoding a presumptive Na+/H+ antiporter), as well as the ndh3 operon encoding the NAD(P)H-dehydrogenase subunits F3 and D3 and a protein of unknown function. The sll1594 gene and the ndh3 operon are negatively controlled by Sll1594, which also regulates the expression of the slr1727 gene. Sequence alignment of the diverse Sll1594 DNA binding sites led us to propose the TCAATG-(N10)-ATCAAT sequence as the consensus motif. To our knowledge, this is the first report on the characterization and analysis of a transcriptional regulator for ndh genes in a photoautotrophic organism.

[Mutation in the glmS gene responsible for the cell wall synthesis increases resistance to the herbicide amitrole in the cyanobacterium Synechocystis sp. PCC6803]. / Mutatsiia v gene glmS, kontroliruiushchem sintez kletochnoi stenki, povyshaet ustoichivost' k gerbitsidu amitrolu u tsianobakterii Synechocystis sp. PCC6803.

A DNA fragment transforming the cells of the cyanobacterium Synechocystis sp. PCC 6803 to amitrole (3-amino-1,2,4-triazole) resistance was cloned from the Atr2 mutant resistant to this herbicide. The transforming activity of the cloned fragment was shown to be related to the missence-mutation "Val250-->Leu250" in the glmS gene encoding glucosamine-6-phosphate synthase, a key enzyme of cell wall synthesis. The amino acid substitution is localized in the central nonconservative part of the GlmS protein, far from two reaction centers positioned at the ends of a polypeptide. It is suggested that the mutant protein has lost sensitivity to amitrole. In the wild type strain, this herbicide causes conditional glucosamine auxotrophy (exogenous glucosamine restores ability of the cells to row in the presence of the lethal amitrole concentrations). Val250 is proposed to be allosteric binding site of AM in the GlmS protein of cyanobacterium.

Anaerobiosis-specific interaction of tobacco nuclear factors with cis-regulatory sequences in the maize GapC4 promoter.

The promoter of the maize glyceraldehyde-3-phosphate dehydrogenase 4 gene (GapC4) confers strong, specific and ubiquitous anaerobic reporter gene expression in tobacco. To identify factors required for heterologous anaerobic gene expression, 19 progressive 5' and 3' promoter deletions were linked to a chimeric GapC4 TATA box-beta-glucuronidase (GUS) reporter gene construct and transformed into tobacco. In all transgenic lines aerobic expression values were in the range obtained for negative controls while histochemical GUS assays reveal some weak expression in roots only. Anaerobic induction of about 100-fold to more than 1000-fold above unspecific background is mediated by a region of about 190 bp of the GapC4 promoter. Anaerobic reporter gene induction strongly decreases upon deletion of a 20 bp fragment from -286 to -266 relative to the transcription start point. This fragment harbours putative cis-acting sequences. Electrophoretic mobility shift assays with a 50 bp fragment harbouring these cis sequences reveal a high-mobility complex that is formed with nuclear extracts from aerobic and anaerobic leaf tissue while an additional low-mobility complex is anaerobiosis-specific. The formation of the high-mobility complex requires the sequence GTGGGCCCG. The 50 bp fragment alone confers weak and orientation-dependent anaerobic induction to a GapC4 TATA box-beta-glucuronidase (GUS) reporter gene.

The carbon metabolism-controlled Synechocystis gap2 gene harbours a conserved enhancer element and a Gram-positive-like -16 promoter box retained in some chloroplast genes.

The two glyceraldehyde-3-phosphate dehydrogenase-encoding genes (gap) of Synechocystis were shown to be expressed as monocistronic transcripts. Whereas gap1 expression is slow and weak, gap2 gene induction is rapid and strong. Transcription of the gap2 gene was shown to depend on functional photosynthetic electron transport and on active carbon metabolism. The basal promoter of gap2 (P, -45 to +34, relative to the transcription start site) is controlled by three cis-acting elements designated A (-443 to -45), B (+34 to +50, in the untranslated leader region) and C (+50 to +167, in the coding region) that, together, promote a 100-fold stimulation of P activity. Element B was found to behave as a transcriptional enhancer, in that it was active regardless of its position, orientation and distance relative to P. All three cis-acting stimulatory elements exhibit a common 5'-agaTYAACg-3' nucleotide motif that appears to be conserved in cyanobacteria and may be the target for a transcriptional enhancer. We also report that gap2 transcription depends on a Gram-positive-like -16 promoter box (5'-TRTG-3') that was obviously conserved throughout the evolution of chloroplasts. This is the first report on the occurrence of a -16 promoter element in photoautotrophic organisms.

Compartment-specific isoforms of TPI and GAPDH are imported into diatom mitochondria as a fusion protein: evidence in favor of a mitochondrial origin of the eukaryotic glycolytic pathway.

Glyceraldehyde-3-phosphate dehydrogenase (GAPDH) and triosephosphate isomerase (TPI) are essential to glycolysis, the major route of carbohydrate breakdown in eukaryotes. In animals and other heterotrophic eukaryotes, both enzymes are localized in the cytosol; in photosynthetic eukaryotes, GAPDH and TPI exist as isoenzymes that function in the glycolytic pathway of the cytosol and in the Calvin cycle of chloroplasts. Here, we show that diatoms--photosynthetic protists that acquired their plastids through secondary symbiotic engulfment of a eukaryotic rhodophyte--possess an additional isoenzyme each of both GAPDH and TPI. Surprisingly, these new forms are expressed as an TPI-GAPDH fusion protein which is imported into mitochondria prior to its assembly into a tetrameric bifunctional enzyme complex. Homologs of this translational fusion are shown to be conserved and expressed also in nonphotosynthetic, heterokont-flagellated oomycetes. Phylogenetic analyses show that mitochondrial GAPDH and its N-terminal TPI fusion branch deeply within their respective eukaryotic protein phylogenies, suggesting that diatom mitochondria may have retained an ancestral state of glycolytic compartmentation that existed at the onset of mitochondrial symbiosis. These findings strongly support the view that nuclear genes for enzymes of glycolysis in eukaryotes were acquired from mitochondrial genomes and provide new insights into the evolutionary history (host-symbiont relationships) of diatoms and other heterokont-flagellated protists.

Glyceraldehyde-3-phosphate dehydrogenase gene diversity in eubacteria and eukaryotes: evidence for intra- and inter-kingdom gene transfer.

Cyanobacteria contain up to three highly divergent glyceraldehyde-3-phosphate dehydrogenase (GAPDH) genes: gap1, gap2, and gap3. Genes gap1 and gap2 are closely related at the sequence level to the nuclear genes encoding cytosolic and chloroplast GAPDH of higher plants and have recently been shown to play distinct key roles in catabolic and anabolic carbon flow, respectively, of the unicellular cyanobacterium Synechocystis sp. PCC6803. In the present study, sequences of 10 GAPDH genes distributed across the cyanobacteria Prochloron didemni, Gloeobacter violaceus PCC7421, and Synechococcus PCC7942 and the alpha-proteobacterium Paracoccus denitrificans and the beta-proteobacterium Ralstonia solanacearum were determined. Prochloron didemni possesses homologs to the gap2 and gap3 genes from Anabaena, Gloeobacter harbors gap1 and gap2 homologs, and Synechococcus possesses gap1, gap2, and gap3. Paracoccus harbors two highly divergent gap genes that are related to gap3, and Ralstonia possesses a homolog of the gap1 gene. Phylogenetic analyses of these sequences in the context of other eubacterial and eukaryotic GAPDH genes reveal that divergence across eubacterial gap1, and gap2, and gap3 genes is greater than that between eubacterial gap1 and eukaroytic glycolytic GapC or between eubacterial gap2 and eukaryotic Calvin cycle GapAB. These data strongly support previous analyses which suggested that eukaryotes acquired their nuclear genes for GapC and GapAB via endosymbiotic gene transfer from the antecedents of mitochondria and chloroplasts, and extend the known range of sequence diversity of the antecedent eubacterial genes. Analyses of available GAPDH sequences from other eubacterial sources indicate that the glycosomal gap gene from trypanosomes (cytosolic in Euglena) and the gap gene from the spirochete Treponema pallidum are each other's closest relatives. This specific relationship can therefore not reflect organismal evolution but must be the result of an interkingdom gene transfer, the direction of which cannot be determined with certainty at present. Contrary to this, the origin of the cytosolic Gap gene from trypanosomes can now be clearly defined as gamma-proteobacterial, since the newly established Ralstonia sequence (beta-proteobacteria) branches basally to the gamma-proteobacterial/trypanosomal assemblage.

Structure and evolution of Cyclops: a novel giant retrotransposon of the Ty3/Gypsy family highly amplified in pea and other legume species.

We characterized a novel giant Gypsy-like retrotransposon, Cyclops, present in about 5000 copies in the genome of Pisum sativum. The individual element Cyclops-2 measures 12 314 bp including long terminal repeats (LTRs) of 1504 bp and 1594 bp, respectively, showing 4.1% sequence divergence between one another. Cyclops-2 carries a polypurine tract (PPT) and an unusual primer binding site (PBS) complementary to tRNA-Glu. The element is bounded by 5 bp target site duplications and harbors three successive internal regions with homology to retroviral genes gag (424 codons) and pol (1382 codons) and an additional open reading frame (423 codons) of unknown function indicating the element's potential capacity for gene transduction. The pol region contains sequence motifs related to the enzymes protease, reverse transcriptase, RNAse H and integrase in the same typical order (5'-PR-RT-RH-IN-3') known for retroviruses and Gypsy-like retrotransposons. The reading frame of the pol region is disrupted by several mutations suggesting that Cyclops-2 does not encode functional enzymes. A phylogenetic analysis of the reverse transcriptase domain confirms our differential genetic assessment that Cyclops from pea is a novel element with no specific relationship to the previously described Gypsy-like elements from plants. Genomic Southern hybridizations show that Cyclops is abundant not only in pea but also in common bean, mung bean, broad bean, soybean and the pea nut suggesting that Cyclops may be an useful genetic tool for analyzing the genomes of agronomically important legumes.

Gene structure, expression in Escherichia coli and biochemical properties of the NAD+ -dependent glyceraldehyde-3-phosphate dehydrogenase from Pinus sylvestris chloroplasts.

Photosynthetic eukaryotes typically possess two distinct glyceraldehyde-3-phosphate dehydrogenases, an NAD+ -specific enzyme in the cytosol (GapC: EC 1.2.1.12) and an NADP+ -dependent enzyme in the chloroplast (GapAB: EC 1.2.1.13). The gymnosperm Pinus sylvestris is an exception in that it is known to express a gene encoding a transit peptide-bearing GapC-like subunit that is imported into chloroplasts (GapCp), but the enzymatic properties of this novel GAPDH have not been described from any source. We have expressed the mature GapCp unit from Pinus in Escherichia coli and have characterized the active enzyme. GapCp has a specific activity of 89 units per milligram and is strictly NAD+ -dependent, showing no detectable activity with NADP+. Values of the apparent Km for NAD+ and glyceraldehyde-3-phosphate were determined as 62 and 344 microM, respectively. The Pinus GapCpl gene possesses 12 introns, two in the region encoding the transit peptide and ten in the region encoding the mature subunit, all of which are found at positions strictly conserved across genes for higher plant GapC. A cDNA encoding a homologue of GapCp was isolated from the heterosporous fern Marsilea quadrifolia, indicating that NAD+ -dependent chloroplast GAPDH also occurs in other higher plants.

Genetic and biochemical evidence for distinct key functions of two highly divergent GAPDH genes in catabolic and anabolic carbon flow of the cyanobacterium Synechocystis sp. PCC 6803.

Cyanobacterial genomes harbour two separate highly divergent glyceraldehyde-3-phosphate dehydrogenase (GAPDH) genes, gap1 and gap2, which are closely related at the sequence level to the nuclear genes encoding cytosolic and chloroplast GAPDH of higher plants, respectively. Genes gap1 and gap2 of the unicellular cyanobacterium Synechocystis sp. PCC 6803 were cloned and sequenced and subsequently inactivated by insertional mutagenesis to understand their metabolic functions. We obtained homozygous gap1- mutants which have lost the capacity to grow on glucose under dim light while growth on organic acids as well as photosynthetic growth under CO2 and high light is not impaired. Homozygous gap2- mutants show the reciprocal phenotype. Under dim light they only grow on glucose but not on organic acids nor do they survive under photosynthetic conditions. Measurements of the anabolic activities (reduction of 1,3-bisphosphoglycerate) in extracts from wild type and mutant cells show that Gap2 is a major enzyme with dual cosubstrate specificity for NAD and NADP, while Gap1 displays a minor NAD-specific GAPDH activity. However, if measured in the catabolic direction (oxidation of glyceraldehyde-3-phosphate) Gap2 activity is very low and increases three- to fivefold after gel filtration of extracts over Sephadex G25. Our results suggest that enzymes Gap1 and Gap2, although coexpressed in cyanobacterial wild-type cells, play distinct key roles in catabolic and anabolic carbon flow, respectively. While Gap2 operates in the photosynthetic Calvin cycle and in non-photosynthetic gluconeogenesis, Gap1 seems to be essential only for glycolytic glucose breakdown, conditions under which the catabolic activity of Gap2 seems to be repressed by a specific low-molecular-weight inhibitor.

Sequence of the non-phosphorylating glyceraldehyde-3-phosphate dehydrogenase from Nicotiana plumbaginifolia and phylogenetic origin of the gene family.

A cDNA-library has been constructed from Nicotiana plumbaginifolia seedlings, and the non-phosphorylating glyceraldehyde-3-phosphate dehydrogenase (GapN, EC 1.2.1.9) was isolated by plaque hybridization using the cDNA from pea as a heterologous probe. The cDNA comprises the entire GapN coding region. A putative polyadenylation signal is identified. Phylogenetic analysis based on the deduced amino acid sequences revealed that the GapN gene family represents a separate ancient branch within the aldehyde dehydrogenase superfamily. It can be shown that the GapN gene family and other distinct branches of the superfamily have its phylogenetic origin before the separation of primary life-forms. This further demonstrates that already very early in evolution, a broad diversification of the aldehyde dehydrogenases led to the formation of the superfamily.

Evolutionary origin of cryptomonad microalgae: two novel chloroplast/cytosol-specific GAPDH genes as potential markers of ancestral endosymbiont and host cell components.

Cryptomonads are complex microalgae which share characteristics of chromophytes (chlorophyll c, extra pair of membranes surrounding the plastids) and rhodophytes (phycobiliproteins). Unlike chromophytes, however, they contain a small nucleus-like organelle, the nucleomorph, in the periplastidial space between the inner and outer plastid membrane pairs. These cellular characteristics led to the suggestion that cryptomonads may have originated via a eukaryote-eukaryote endosymbiosis between a phagotrophic host cell and a unicellular red alga, a hypothesis supported by rRNA phylogenies. Here we characterized cDNAs of the nuclear genes encoding chloroplast and cytosolic glyceraldehyde-3-phosphate dehydrogenases (GAPDH) from the two cryptomonads Pyrenomonas salina and Guillardia theta. Our results suggest that in cryptomonads the classic Calvin cycle GAPDH enzyme of cyanobacterial origin, GapAB, is absent and functionally replaced by a photosynthetic GapC enzyme of proteobacterial descent, GapC1. The derived GapC1 precursor contains a typical signal/transit peptide of complex structure and sequence signatures diagnostic for dual cosubstrate specificity with NADP and NAD. In addition to this novel GapC1 gene a cytosol-specific GapC2 gene of glycolytic function has been found in both cryptomonads showing conspicuous sequence similarities to animal GAPDH. The present findings support the hypothesis that the host cell component of cryptomonads may be derived from a phototrophic rather than a organotrophic cell which lost its primary plastid after receiving a secondary one. Hence, cellular compartments of endosymbiotic origin may have been lost or replaced several times in eukaryote cell evolution, while the corresponding endosymbiotic genes (e.g., GapC1) were retained, thereby increasing the chimeric potential of the nuclear genome.

Functional studies of chloroplast glyceraldehyde-3-phosphate dehydrogenase subunits A and B expressed in Escherichia coli: formation of highly active A4 and B4 homotetramers and evidence that aggregation of the B4 complex is mediated by the B subunit carboxy terminus.

Chloroplast glyceraldehyde-3-phosphate dehydrogenase (phosphorylating, E.C. 1.2.1.13) (GAPDH) of higher plants exists as an A2B2 heterotetramer that catalyses the reductive step of the Calvin cycle. In dark chloroplasts the enzyme exhibits a molecular mass of 600 kDa, whereas in illuminated chloroplasts the molecular mass is altered in favor of the more active 150 kDa form. We have expressed in Escherichia coli proteins corresponding to the mature A and B subunits of spinach chloroplast GAPDH (GapA and GapB, respectively) in addition to a derivative of the B subunit lacking the GapB-specific C-terminal extension (CTE). One mg of each of the three proteins so expressed was purified to electrophoretic homogeneity with conventional methods. Spinach GapA purified from E. coli is shown to be a highly active homotetramer (50-70 U/mg) which does not associate under aggregating conditions in vitro to high-molecular-mass (HMM) forms of ca. 600 kDa. Since B4 forms of the enzyme have not been described from any source, we were surprised to find that spinach GapB purified from E. coli was active (15-35 U/mg). Spinach GapB lacking the CTE purified from E. coli is more highly active (130 U/mg) than GapB with the CTE. Under aggregating conditions, GapB lacking the CTE is a tetramer that does not associate to HMM forms whereas GapB with the CTE occurs exclusively as an aggregated HMM form. The data indicate that intertetramer association of chloroplast GAPDH in vitro occurs through GapB-mediated protein-protein interaction.

Intron-specific stimulation of anaerobic gene expression and splicing efficiency in maize cells.

Most of the glyceraldehyde-3-phosphate dehydrogenase (GAPDH) genes characterized in plants and algae to date have one intron very close to the 5' end of the gene. To study the functional relevance of some of these introns for gene expression we have analysed the influence of three 5' introns on transient gene expression of the anaerobically inducible maize GapC4 promoter in maize cells. Under aerobic conditions, reporter gene expression is increased in the presence of the first introns of the GapC4 and GapC1 genes, and the first intron of the nuclear encoded chloroplast-specific GapA1 gene. In contrast, the GapC4 intron increases anaerobic gene expression above the level obtained for the intronless construct, while anaerobic expression of constructs harboring the GapA1 and GapC1 introns was similar to the anaerobic expression level of the intronless construct. Splicing analysis revealed that the GapC4 intron is processed more efficiently under anaerobic conditions, while no change in splicing efficiency is observed for the GapC1 and the GapA1 introns when subjected to anaerobic conditions. These results suggest that an increase in splicing efficiency contributes to the anaerobic induction of the maize GapC4 gene.

Transaldolase genes from the cyanobacteria Anabaena variabilis and Synechocystis sp. PCC 6803: comparison with other eubacterial and eukaryotic homologues.

We have sequenced and analysed the transaldolase (tal) genes from two cyanobacteria, Anabaena variabilis (ATCC 29413) and Synechocystis sp. PCC 6803, which are filamentous heterocyst-forming and unicellular organisms, respectively. The deduced amino acid sequences of the two cyanobacterial tal genes are 78% identical and are highly homologous to both eubacterial and eukaryotic transaldolases (Escherichia coli, two yeasts, and man) with values ranging from 54 to 60% amino acid identity. In contrast, the transaldolase homologous sequences from the cyanobacterium Nostoc sp. ATCC 29133, from Mycobacterium leprae, and the partial sequence from the higher plant Arabidopsis thaliana have a much lower degree of homology with each other and relative to the sequences mentioned above. These data indicate three different types of transaldolases.

The maize GapC4 promoter confers anaerobic reporter gene expression and shows homology to the maize anthocyanin regulatory locus C1.

The cytosolic glyceraldehyde-3-phosphate dehydrogenase (GapC) gene family of maize is differentially expressed in response to anaerobic stress. While GapCl and GapC2 are downregulated, GapC3 and GapC4 are anaerobically induced. We have sequenced and analyzed a 3073 bp promoter fragment of GapC4. The promoter confers anaerobic induction of a reporter gene construct in a transient gene expression system in maize. Deletion analysis of the GapC4 promoter revealed a 270 bp long DNA region required for anaerobic induction. This region contains sequence motifs resembling the cis-acting sequences of the anaerobically induced maize Adh1 and Adh2 genes. Furthermore, the 3073 bp GapC4 promoter fragment displays homology to long terminal repeats of maize retrotransposons and to the 3' region of the maize anthocyanin regulatory locus C1.