A cloned cyanobacterial gene for glutamine synthetase functions in Escherichia coli, but the enzyme is not adenylylated

The coding sequence for Anabaena 7120 glutamine synthetase [L-glutamate:ammonia ligase (ADP-forming), EC 6.3.1.1] are shown to be contained within a 7.5-kilobase-pair (kbp) HindIII fragment that has been cloned by plaque hybridization. The hybridization probe for the cyanobacterial gene was a recombinant plasmid containing the glnA gene from Escherichia coli K-12. Evidence that the cloned Anabaena fragment contains the glnA gene includes complementation of a glnA deletion mutant of E. coli and immunological identity of the enzyme produced by the cloned Anabaena fragment in E. coli with glutamine synthetase purified from Anabaena 7120. Heteroduplex analysis reveals 0.65 kbp of homology between the 7.5-kbp Anabaena 7120 fragment and an 11-kbp E. coli fragment that codes for E. coli glutamine synthetase. Studies of Anabaena glnA gene activity in E. coli suggest that the cyanobacterial gene is not repressible and that the Anabaena 7120 glutamine synthetase is not adenylylated in E. coli.     

A gene encoding a protein related to eukaryotic protein kinases from the filamentous heterocystous cyanobacterium Anabaena PCC 7120.

Protein kinases play essential roles in the development of eukaryotic cells. These enzymes display various degrees of sequence similarity in their catalytic domains. This conservation has allowed the identification of protein kinases in a variety of organisms, including the Gram-negative bacterium Myxococcus xanthus. In this study, sequences related to those encoding eukaryotic protein kinases were amplified by PCR from DNA of Anabaena PCC 7120, a filamentous cyanobacterium that differentiates cells specifically for nitrogen fixation, called heterocysts, under conditions of combined nitrogen limitation. Results from Southern hybridization and sequencing of PCR products suggest the presence of a family of similar protein kinases in this strain. One of the corresponding genes (pknA) was isolated from a gene library. The N-terminal region of its amino acid sequence shows significant similarity to the catalytic domains of eukaryotic-type protein kinases. Expression of this gene was found to be developmentally regulated. Inactivation of pknA led to colonies that appeared light green and rough in the absence of combined nitrogen. Mutant filaments produce fewer heterocysts than wild-type ones. These results suggest that pknA is required for both normal cellular growth and differentiation of Anabaena PCC 7120.     

The patA gene product, which contains a region similar to CheY of Escherichia coli, controls heterocyst pattern formation in the cyanobacterium Anabaena 7120.

In Anabaena 7120, heterocysts (cells specialized for nitrogen fixation) develop at the ends of filaments and at intervals within each filament. We have isolated a mutant Anabaena strain that develops heterocysts mostly at the ends of filaments. This mutant, PAT-1, grows poorly under nitrogen-fixing conditions. The wild-type gene that complements the mutation in PAT-1, called patA, was cloned and sequenced. The predicted PatA protein contains 379 amino acids distributed among three "domains" based on predictions of hydropathy and flexibility. The carboxyl-terminal domain is very similar to that of CheY and other response regulators in two-component regulatory systems in eubacteria. The patA mutation suppresses the multiheterocyst phenotype produced by extra copies of the wild-type hetR gene described previously, suggesting that PatA and HetR are components of the same environment-sensing regulatory circuit in Anabaena.     

CcbP, a calcium-binding protein from Anabaena sp. PCC 7120, provides evidence that calcium ions regulate heterocyst differentiation

Although it is known that calcium is a very important messenger involved in many eukaryotic cellular processes, much less is known about calcium's role in bacteria. CcbP, a Ca(2+)-binding protein, was isolated from the heterocystous cyanobacterium Anabaena sp. PCC 7120, and the ccbP gene was cloned and inactivated. In the absence of combined nitrogen, inactivation of ccbP resulted in multiple contiguous heterocysts, whereas overexpression of ccbP suppressed heterocyst formation. Calmodulin, which is not present in Anabaena species, could also suppress heterocyst formation in both Anabaena sp. PCC 7120 and Anabaena variabilis. HetR induction upon nitrogen step-down was slow in the strain overexpressing ccbP. The Ca(2+) reporter protein obelin was used to show that mature heterocysts had a high intracellular free Ca(2+)concentration {[Ca(2+)](i)}, and immunoblotting showed that CcbP was absent from heterocysts. A regular pattern of cells with higher [Ca(2+)](i) was established during heterocyst differentiation before the appearance of proheterocysts. A rapid increase of [Ca(2+)](i) could be detected 4 h after the removal of combined nitrogen, and this increase was suppressed by excessive CcbP. These results suggest that Ca(2+) ions play very important roles in hetR induction and heterocyst differentiation.     

Electron transport to nitrogenase in Klebsiella pneumoniae.

Cell-free extracts of nifF and nifJ mutants of Klebsiella pneumoniae are unable to couple acetylene reduction (N2 fixation) by nitrogenase to the oxidation of organic metabolites. However, nifF and nifJ mutants can complement each other in vitro to establish the coupling. This indicates that the products of the nifF and nifJ genes constitute essential elements of the physiological electron pathway to nitrogenase. The electron-transfer-active product of the nifF gene, a flavoprotein, has been purified.     

HetR homodimer is a DNA-binding protein required for heterocyst differentiation, and the DNA-binding activity is inhibited by PatS

HetR plays a key role in regulation of heterocyst differentiation. When the Cys-48 residue of the HetR from Anabaena sp. PCC 7120 was replaced with an Ala residue, the mutant HetR (HetR(C48A)) could not dimerize, indicating that HetR forms a homodimer through a disulfide bond. The Anabaena strain C48, containing the hetRc48a gene, could not produce HetR homodimer and failed to form heterocyst. We show that HetR is a DNA-binding protein and that its homodimerization is required for the DNA binding. HetR binds the promoter regions of hetR, hepA, and patS, suggesting a direct control of the expression of these genes by HetR. We present evidence that shows that the up-regulation of patS and hetR depends on DNA binding by HetR dimer. The pentapeptide RGSGR, which is present at the C terminus of PatS and blocks heterocyst formation, inhibits the DNA binding of HetR and prevents hetR up-regulation.     

Programmed DNA rearrangement of a cyanobacterial hupL gene in heterocysts.

Programmed DNA rearrangements that occur during cellular differentiation are uncommon and have been described in only two prokaryotic organisms. Here, we identify the developmentally regulated rearrangement of a hydrogenase gene in heterocysts of the cyanobacterium Anabaena sp. strain PCC 7120. Heterocysts are terminally differentiated cells specialized for nitrogen fixation. Late during heterocyst differentiation, a 10.5-kb DNA element is excised from within the hupL gene by site-specific recombination between 16-bp direct repeats that flank the element. The predicted HupL polypeptide is homologous to the large subunit of [NiFe] uptake hydrogenases. hupL is expressed similarly to the nitrogen-fixation genes; hupL message was detected only during the late stages of heterocyst development. An open reading frame, named xisC, identified near one end of the hupL DNA element is presumed to encode the element's site-specific recombinase. The predicted XisC polypeptide is homologous with the Anabaena sp. strain PCC 7120 site-specific recombinase XisA. Neither XisC nor XisA shows sequence similarity to other proteins, suggesting that they represent a different class of site-specific recombinase.     

Identification of blue-green algal nitrogen fixation genes by using heterologous DNA hybridization probes

In the filamentous blue-green alga Anabaena 7120, aerobic nitrogen fixation is linked to the differentiation of specialized cells called heterocysts. In order to study control of heterocyst development and nitrogen fixation in Anabaena, we have used cloned fragments of the Klebsiella pneumoniae nitrogen fixation (nif) genes as probes in DNA·DNA hybridizations with restriction endonuclease fragments of Anabaena DNA. Using this technique, we were able to identify and clone Anabaena nif genes, demonstrating the feasibility of using heterologous probes to identify genes for which no traditional genetic selection exists. From the patterns of hybridization observed, we deduced that although DNA sequence homology has been retained between some of the nif genes of these divergent organisms, the nif gene order has been rearranged.     

Stanniocalcin in the euryhaline flounder (Platichthys flesus): primary structure, tissue distribution, and response to altered salinity

Stanniocalcin (STC) is a homodimeric glycoprotein hormone that was first discovered in fish, where it is largely produced by a unique endocrine gland, the corpuscles of Stannius (CS). In bony fish, it is thought to be an important regulator of calcium and phosphate uptake from the aquatic environment. This report describes the molecular cloning of STC from euryhaline flounder (Platichthys flesus) CS cDNA and genomic DNA. The flounder STC encodes a prehormone of 251 amino acids (aa) with a signal peptide of 17 aa, followed by another 15 aa sequence before the mature protein of 219 aa. The deduced aa sequence of flounder STC shows 62.9-89.0% similarity and 50.4-83.1% identity with other known fish STC sequences, but only 42.3% identity with mouse STC1, 24.4% identity with fugu and zebrafish STC2, and 22.3% identity with mouse STC2. Primary structural analysis demonstrated that flounder STC gene contains five exons in contrast to the four exons present in mammalian STC gene. RT-PCR revealed the expression of flounder STC mRNA to be widely spread in many tissues and organs, similar to the situation in mammals and other fish. Quantitative PCR (Q-PCR) was conducted to measure relative STC expression levels in the CS, which showed STC mRNA expression levels in seawater-adapted fish CS were about 3-fold higher than in freshwater-adapted fish CS.     

Exon-intron organization and sequence comparison of human and murine T11 (CD2) genes.

Genomic DNA clones containing the human and murine genes coding for the 50-kDa T11 (CD2) T-cell surface glycoprotein were characterized. The human T11 gene is approximately equal to 12 kilobases long and comprised of five exons. A leader exon (L) contains the 5'-untranslated region and most of the nucleotides defining the signal peptide [amino acids (aa) -24 to -5]. Two exons encode the extracellular segment; exon Ex1 is 321 base pairs (bp) long and codes for four residues of the leader peptide and aa 1-103 of the mature protein, and exon Ex2 is 231 bp long and encodes aa 104-180. Exon TM is 123 bp long and codes for the single transmembrane region of the molecule (aa 181-221). Exon C is a large 765-bp exon encoding virtually the entire cytoplasmic domain (aa 222-327) and the 3'-untranslated region. The murine T11 gene has a similar organization with exon-intron boundaries essentially identical to the human gene. Substantial conservation of nucleotide sequences between species in both 5'- and 3'-gene flanking regions equivalent to that among homologous exons suggests that murine and human genes may be regulated in a similar fashion. The probable relationship of the individual T11 exons to functional and structural protein domains is discussed.     

Anabaena sensory rhodopsin is a light-driven unidirectional rotor

The implementation of multiconfigurational quantum chemistry methods into a quantum-mechanics/molecular-mechanics protocol has allowed the construction of a realistic computer model for the sensory rhodopsin of the cyanobacterium Anabaena PCC 7120. The model, which reproduces the absorption spectra of both the all-trans and 13-cis forms of the protein and their associated K and L intermediates, is employed to investigate the light-driven steps of the photochromic cycle exhibited by the protein. It is found that the photoisomerizations of the all-trans and 13-cis retinal chromophores occur through unidirectional, counterclockwise 180° rotations of the =C14-C15= moiety with respect to the Lys210-linked end of the chromophore axis. Thus, the sequential interconversions of the all-trans and 13-cis forms during a single photochromic cycle yield a complete (360°) unidirectional rotation of the =C14-C15= moiety. This finding implies that Anabaena sensory rhodopsin is a biological realization of a light-driven molecular rotor.     

Recurrence of 49-base decamers, nonomers, and octamers within mouse C mu gene of Ig heavy chain and its primordial building block.

Within the published 2,168-base-long mouse C mu gene of Ig heavy chain consisting of four coding and four noncoding segments, 2 base decamers, 8 nonomers, and 39 octamers recurred. Recurring base heptamers (about 100) and hexamers (about 350) were simply too numerous to merit individual identification. In spite of extensive overlaps between these recurring base decamers to hexamers, they occupied nearly the entire length of mouse Ig C mu gene. As with other genes of the beta-sheet-forming beta 2-microglobulin family, the Ig C mu gene (flanking and intervening noncoding sequences included) is not a unique sequence but rather it is degenerate repeats of the 45-base-long primordial building-block sequence uniquely its own. This primordial building block must originally have specified the 15-amino-acid-residue-long primordial arm of beta-sheet-forming loops, the characteristics of the beta 2-microglobulin family of polypeptides.     

An essential member of the HSP70 gene family of Saccharomyces cerevisiae is homologous to immunoglobulin heavy chain binding protein.

Immunoglobulin heavy chain binding protein (BiP) is present in the lumen of the mammalian endoplasmic reticulum, where it associates transiently with a variety of newly synthesized secretory and membrane proteins or permanently with mutant proteins that are incorrectly folded. We describe a unique member of the Saccharomyces cerevisiae 70-kDa heat shock protein gene family (HSP70) that encodes a protein homologous to mammalian BiP. The DNA sequence contains a 2046-nucleotide open reading frame devoid of introns, and examination of the predicted amino acid sequence reveals features not found in most other yeast HSP70 proteins but which are present in BiP. Most notable are a 42-residue sequence at the N terminus that exhibits characteristics of a cleavable signal sequence and a C-terminal sequence, -His-Asp-Glu-Leu, that is involved in determining endoplasmic reticulum localization in yeast. The 5' flanking region of this gene contains two overlapping sequences between nucleotides -146 and -169 that closely resemble consensus heat shock elements. The yeast BiP gene is strongly heat shock-inducible, whereas the BiP genes in various other species are either weakly or non-heat-inducible. We demonstrate that a functional BiP gene is essential for vegetative growth. An evolutionary comparison of amino acid sequences of 34 HSP70 proteins from 17 species suggests that BiP genes share a common ancestor, which diverged from other HSP70 genes near the time when eukaryotes first appeared.     

The protein deficient in Lowe syndrome is a phosphatidylinositol-4,5-bisphosphate 5-phosphatase.

Lowe syndrome, also known as oculocerebrorenal syndrome, is caused by mutations in the X chromosome-encoded OCRL gene. The OCRL protein is 51% identical to inositol polyphosphate 5-phosphatase II (5-phosphatase II) from human platelets over a span of 744 aa, suggesting that OCRL may be a similar enzyme. We engineered a construct of the OCRL cDNA that encodes amino acids homologous to the platelet 5-phosphatase for expression in baculovirus-infected Sf9 insect cells. This cDNA encodes aa 264-968 of the OCRL protein. The recombinant protein was found to catalyze the reactions also carried out by platelet 5-phosphatase II. Thus OCRL converts inositol 1,4,5-trisphosphate to inositol 1,4-bisphosphate, and it converts inositol 1,3,4,5-tetrakisphosphate to inositol 1,3,4-trisphosphate. Most important, the enzyme converts phosphatidylinositol 4,5-bisphosphate to phosphatidylinositol 4-phosphate. The relative ability of OCRL to catalyze the three reactions is different from that of 5-phosphatase II and from that of another 5-phosphatase isoenzyme from platelets, 5-phosphatase I. The recombinant OCRL protein hydrolyzes the phospholipid substrate 10- to 30-fold better than 5-phosphatase II, and 5-phosphatase I does not cleave the lipid at all. We also show that OCRL functions as a phosphatidylinositol 4,5-bisphosphate 5-phosphatase in OCRL-expressing Sf9 cells. These results suggest that OCRL is mainly a lipid phosphatase that may control cellular levels of a critical metabolite, phosphatidylinositol 4,5-bisphosphate. Deficiency of this enzyme apparently causes the protean manifestations of Lowe syndrome.     

日本血吸虫中国大陆株基因重组抗原Sj 22.6kDa的核苷酸序列分析

目的：对ｐＧＳｊ２４克隆化基因进行核苷酸序列分析，了解其编码蛋白的属性。方法：常规制备ｐＧＳｊ２４克隆化基因并重组入测序载体Ｍ１３ｍｐ１９，以ＤＹＥＰＲＩＭＥＲ荧光测序试剂盒进行核苷酸序列测定。分别以ＤＮＡＳＩＳ和ＧＯＬＤＫＥＹ软件对序列资料进行分析。结果：ｐＧＳｊ２４克隆化基因长８４０ｂｐ，含一开放阅读框，可编码一分子量为２２．６ｋＤａ的蛋白质。开读框上游和下游均有终止密码子。该基因与已发表的日本血吸虫２２．６ｋＤａ蛋白的编码基因同源性达９５％，编码区同源性达９９．７％。在该基因内有一段典型的ＥＦ－Ｈａｎｄ钙结合区序列，并有内质网导肽、微体导向信号等功能位点。预测该蛋白质内可能的抗原决定簇位置为第２９－３２、６３－６８和８７－１０１等氨基酸片段。结论：ｐＧＳｊ２４克隆化基因为日本血吸虫２２．６ｋＤａ抗原编码基因。     

Nonmetabolizable analogue of 2-oxoglutarate elicits heterocyst differentiation under repressive conditions in Anabaena sp. PCC 7120

In response to combined nitrogen starvation in the growth medium, the filamentous cyanobacterium Anabaena sp. PCC 7120 is able to develop a particular cell type, called a heterocyst, specialized in molecular nitrogen fixation. Heterocysts are regularly intercalated among vegetative cells and represent 5-10% of all cells along each filament. In unicellular cyanobacteria, the key Krebs cycle intermediate, 2-oxoglutarate (2-OG), has been suggested as a nitrogen status signal, but in vivo evidence is still lacking. In this study we show that nitrogen starvation causes 2-OG to accumulate transiently within cells of Anabaena PCC 7120, reaching a maximal intracellular concentration of approximately 0.1 mM 1 h after combined nitrogen starvation. A nonmetabolizable fluorinated 2-OG derivative, 2,2-difluoropentanedioic acid (DFPA), was synthesized and used to demonstrate the signaling function of 2-OG in vivo. DFPA is shown to be a structural analogue of 2-OG and the process of its uptake and accumulation in vivo can be followed by (19)F magic angle spinning NMR because of the presence of the fluorine atom and its chemical stability. DFPA at a threshold concentration of 0.3 mM triggers heterocyst differentiation under repressing conditions. The multidisciplinary approaches using synthetic fluorinated analogues, magic angle spinning NMR for their analysis in vivo, and techniques of molecular biology provide a powerful means to identify the nature of the signals that remain unknown or poorly defined in many signaling pathways.     

日本血吸虫中国大陆株基因重组抗原Sj 22.6kDa的核苷酸序列分析

目的：对ｐＧＳｊ２４克隆化基因进行核苷酸序列分析，了解其编码蛋白的属性。方法：常规制备ｐＧＳｊ２４克隆化基因并重组入测序载体Ｍ１３ｍｐ１９，以ＤＹＥＰＲＩＭＥＲ荧光测序试剂盒进行核苷酸序列测定。分别以ＤＮＡＳＩＳ和ＧＯＬＤＫＥＹ软件对序列资料进行分析。结果：ｐＧＳｊ２４克隆化基因长８４０ｂｐ，含一开放阅读框，可编码一分子量为２２．６ｋＤａ的蛋白质。开读框上游和下游均有终止密码子。该基因与已发表的日本血吸虫２２．６ｋＤａ蛋白的编码基因同源性达９５％，编码区同源性达９９．７％。在该基因内有一段典型的ＥＦ－Ｈａｎｄ钙结合区序列，并有内质网导肽、微体导向信号等功能位点。预测该蛋白质内可能的抗原决定簇位置为第２９－３２、６３－６８和８７－１０１等氨基酸片段。结论：ｐＧＳｊ２４克隆化基因为日本血吸虫２２．６ｋＤａ抗原编码基因。     

Species specificity of human interleukin-3 demonstrated by cloning and expression of the homologous rhesus monkey (Macaca mulatta) gene

To enable preclinical studies on homologous interleukin-3 (IL-3) in primate species, we isolated the gene encoding Rhesus monkey IL-3 (RhIL-3). The nucleotide sequence of the RhIL-3 gene displayed 92.9% homology with that of the human IL-3 (hIL-3) gene. The isolated RhIL-3 gene encodes a 143-amino acid (aa) precursor polypeptide, nine C-terminal residues shorter than the human protein. Protein homology was found to be 89.5% for the signal peptide (19 aa) and 80.5% for the mature protein (124 aa). Comparison of the human and RhIL-3 coding sequences showed that the majority of substitutions had occurred at amino acid replacement sites indicating a rapid evolution of the IL-3 protein. After expression of a genomic fragment in COS cells, RhIL-3 cDNA was constructed, which enabled large-scale production of the RhIL-3 polypeptide, RhIL-3 produced by Bacillus licheniformis and purified to homogeneity appeared to be approximately 100-fold more effective in stimulating Rhesus monkey hematopoietic progenitors than hIL-3, whereas RhIL-3 and hIL-3 showed comparable stimulatory activity on normal as well as malignant human hematopoietic cells. Thus, the rapid evolution of hIL-3 has resulted in a unidirectional species specificity, which most likely restricts the in vivo effects of hIL-3 in Macaca species.     

Different functions of HetR, a master regulator of heterocyst differentiation in Anabaena sp. PCC 7120, can be separated by mutation

The HetR protein has long been recognized as a key player in the regulation of heterocyst development. HetR is known to possess autoproteolytic and DNA-binding activities. During a search for mutants of Anabaena sp. PCC 7120 that can overcome heterocyst suppression caused by overexpression of the patS gene, which encodes a negative regulator of differentiation, a bypass mutant strain, S2-45, was isolated that produced a defective pattern (Pat phenotype) of irregularly spaced single and multiple contiguous heterocysts (Mch phenotype) in combined nitrogen-free medium. Analysis of the S2-45 mutant revealed a R223W mutation in HetR, and reconstruction in the wild-type background showed that this mutation was responsible for the Mch phenotype and resistance not only to overexpressed patS, but also to overexpressed hetN, another negative regulator of differentiation. Ectopic overexpression of the hetRR223W allele in the hetRR223W background resulted in a conditionally lethal (complete differentiation) phenotype. Analysis of the heterocyst pattern in the hetRR223W mutant revealed that heterocysts differentiate essentially randomly along filaments, indicating that this mutation results in an active protein that is insensitive to the major signals governing heterocyst pattern formation. These data provide genetic evidence that, apart from being an essential activator of differentiation, HetR plays a central role in the signaling pathway that controls the heterocyst pattern.