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  • 1
    ISSN: 1432-1432
    Keywords: Key words: Adaptin — Clathrin — Endomembrane system — Eukaryotic evolution — Gene duplication — Multigene family — Phylogeny — Vesicular transport
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract. Eukaryotic vesicular transport requires the recognition of membranes through specific protein complexes. The heterotetrameric adaptor protein complexes 1, 2, and 3 (AP1/2/3) are composed of two large, one small, and one medium adaptin subunit. We isolated and characterized the cDNA for Arabidopsisγ-adaptin and performed a phylogenetic analysis of all adaptin subunits (proteins) in the context of all known homologous proteins. This analysis revealed (i) that the large subunits of AP1/2/3 are homologous and (ii) two subunits of the heptameric coatomer I (COPI) complex belong to this gene family. In addition, all small subunits and the aminoterminal domain of the medium subunits of the heterotetramers are homologous to each other; this also holds for two corresponding subunits of the COPI complex. AP1/2/3 and a substructure (heterotetrameric, F-COPI subcomplex) of the heptameric COPI had a common ancestral complex (called pre-F-COPI). Since all large and all small/medium subunits share sequence similarity, the ancestor of this complex is inferred to have been a heterodimer composed of one large and one small subunit. The situation encountered today is the result of successive rounds of coordinated gene duplications of both the large and the small/medium subunits, with F-COPI being the first that separated from the ancestral pre-F-COPI.
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  • 2
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: Fourteen Rhodobacter capsulatus mutants unable to grow with xanthine as sole nitrogen source were isolated by random Tn5 mutagenesis. Five of these Tn5 insertions were mapped within two adjacent chromosomal EcoRI fragments hybridizing to oligonucleotides synthesized according to conserved amino acid sequences of eukaryotic xanthine dehydrogenases. DNA sequence analysis of this region revealed two open reading frames, designated xdhA and xdhB, encoding xanthine dehydrogenase. The deduced amino acid sequence of XDHA contains binding sites for two [2Fe–2S] clusters and FAD, whereas XDHB is predicted to contain the molybdopterin cofactor. In contrast to R. capsulatus, these three cofactor binding sites reside within a single polypeptide chain in eukaryotic xanthine dehydrogenases. The amino acid sequence of xanthine dehydrogenase from R. capsulatus showed a higher degree of similarity to eukaryotic xanthine dehydrogenases than to the xanthine dehydrogenase-related aldehyde oxidoreductase from Desulphovibrio gigas. The expression of an xdhA–lacZ fusion was induced when hypoxanthine or xanthine was added as sole nitrogen source. Mutations in nifR1 (ntrC) and nifR4 (rpoN, encoding σ54) had no influence on xdh gene expression. A putative activator sensing the availability of substrate seems to respond to xanthine but not to hypoxanthine. The transcriptional start site of xdhA was mapped by primer extension analysis. Comparison with known promoter elements revealed no significant homology. Xanthine dehydrogenase from R. capsulatus was purified to homogeneity. The enzyme consists of two subunits with molecular masses of 85 kDa and 50 kDa respectively. N-terminal amino acid sequencing of both subunits confirmed the predicted start codons. The molecular mass of the native enzyme was determined to be 275 kDa, indicating an α2β2-subunit structure. Analysis of the molybdenum cofactor of xanthine dehydrogenase from R. capsulatus revealed that it contains the molybdopterin cofactor and not a molybdopterin dinucleotide derivative.
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  • 3
    ISSN: 1574-6968
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Molybdenum is an important trace element as it forms the essential part of the active site in all molybdenum-containing enzymes. We have designed an assay for the in vivo detection of molybdate binding to proteins in Escherichia coli. The assay is based on (i) the molybdate-dependent transcriptional regulation of the moa operon by the ModE protein, and (ii) the competition for molybdate between ModE and other molybdate-binding proteins in the cytoplasm of E. coli. We were able to verify in vivo molybdate binding to three different bacterial proteins that are known to bind molybdate. This sensitive in vivo system allows the testing of different proteins for molybdate binding under in vivo conditions and will facilitate the identification of other cellular factors needed for molybdate binding. As a first example, we examined the eukaryotic protein Cnx1 that is involved in the last step of molybdenum cofactor biosynthesis in plants, and show that it is able to compete with ModE for molybdate in a molybdopterin-dependent fashion.
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  • 4
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] The molybdenum cofactor is part of the active site of all molybdenum-dependent enzymes, except nitrogenase. The molybdenum cofactor consists of molybdopterin, a phosphorylated pyranopterin, with an ene-dithiolate coordinating molybdenum. The same pyranopterin-based cofactor is involved in metal ...
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  • 5
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Physiologia plantarum 98 (1996), S. 0 
    ISSN: 1399-3054
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Electroporation was used to introduce DNA into excised scutella of immature embryos of Hordeum vulgare L. cvs Golden Promise and Delita. Using the firefly luciferase gene as reporter, parameters were analyzed for high transient gene expression while maintaining tissue viability. Enzymatic wounding was necessary for DNA uptake. The optimized protocol involves use of linearized DNA and addition of 15% (w/v) polyethylene glycol at a field strength of 950 V cm−1 and approximately 56 ms pulse length. A one-day preculture was required for obtaining callus after electroporation. Transient gene expression was further demonstrated using the β-glucuronidase gene. Blue spots were detected at the abaxial scutellar surface, indicating that cells competent for somatic embryogenesis are also amenable to transfection by electroporation.
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  • 6
    Electronic Resource
    Electronic Resource
    Springer
    Molecular genetics and genomics 251 (1996), S. 252-258 
    ISSN: 1617-4623
    Keywords: Key words Anaerobiosis ; Glyceraldehyde-3-phosphate dehydrogenase ; Introns ; Transientgene expression ; Zea mays
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract  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.
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  • 7
    ISSN: 1546-1718
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Medicine
    Notes: [Auszug] All molybdoenzymes other than nitrogenase require molybdopterin as a metal-binding cofactor. Several genes necessary for the synthesis of the molybdenum cofactor (MoCo) have been characterized in bacteria and plants. The proteins encoded by the Escherichia coli genes moaA and moaC catalyse the ...
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  • 8
    Electronic Resource
    Electronic Resource
    Springer
    Planta 203 (1997), S. 399-405 
    ISSN: 1432-2048
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
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  • 9
    ISSN: 1432-2048
    Keywords: Molybdenum ; Mutant (Nicotiana) ; Nicotiana (nitrate reductase) ; Nitrate reductase mutant
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Two nitrate reductase-deficient mutant cell lines (CnxA68/2, CnxA101) of Nicotiana tabacum are shown to be repairable under in-vitro conditions by (i) molybdate or (ii) by preparations of active molybdenum cofactor of homologous or heterologous origin, thereby yielding about 20% and 80%, respectively, of the corresponding wild-type NADH-nitrate reductase (EC 1.6.6.1) activity. In-vitro repair of nitrate reductase activity is dependent on sulphydryl-group protecting reagents and ethylenediaminetetraacetic acid (EDTA) in the extraction medium, the nitrogen source in the growth medium and the age of the cells. The results support the conclusion that the cnxA gene controls the insertion of molybdenum into the molybdenum cofactor. They are consistent with the idea of two interlinked pathways for the metabolic processing of molybdenum acquisition, one involving the synthesis of the structural moiety of the molybdenum cofactor and the other involving processing of the molybdate anion.
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  • 10
    ISSN: 1573-5028
    Keywords: anaerobiosis ; BMS cells ; glyceraldehyde-3-phosphate dehydrogenase ; transient gene expression ; Zea mays
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The cytosolic glyceraldehyde-3-phosphate dehydrogenase (GapC) gene family of maize is differentially expressed in response to anaerobic stress. While GapC1 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.
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