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Abstract
The appearance and the significance of heuristically developed bonding models are compared with the phenomenon of unicorns in mythical saga. It is argued that classical bonding models played an essential role for the development of the chemical science providing the language which is spoken in the territory of chemistry. The advent and the further development of quantum chemistry demands some restrictions and boundary conditions for classical chemical bonding models, which will continue to be integral parts of chemistry.
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Frenking G, Krapp A, Nagase S, Takagi N, Sekiguchi A. Comment on “Disproving a Silicon Analog of an Alkyne with the Aid of Topological Analyses of the Electronic Structure and Ab Initio Molecular Dynamics Calculations”. Chemphyschem 2006; 7:799-800; author reply 801-2. [PMID: 16596606 DOI: 10.1002/cphc.200500689] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
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Frenking G, Loschen C, Krapp A, Fau S, Strauss SH. Electronic structure of CO—An exercise in modern chemical bonding theory. J Comput Chem 2006; 28:117-26. [PMID: 16917855 DOI: 10.1002/jcc.20477] [Citation(s) in RCA: 97] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
This paper discusses recent progress that has been made in the understanding of the electronic structure and bonding situation of carbon monoxide which was analyzed using modern quantum chemical methods. The new results are compared with standard models of chemical bonding. The electronic charge distribution and the dipole moment, the nature of the HOMO and the bond dissociation energy are discussed in detail.
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Cappel D, Tüllmann S, Krapp A, Frenking G. Direkte Bestimmung der konjugativen und hyperkonjugativen Stabilisierung in Diinen, Dienen und verwandten Verbindungen. Angew Chem Int Ed Engl 2005. [DOI: 10.1002/ange.200500452] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
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Cappel D, Tüllmann S, Krapp A, Frenking G. Direct Estimate of the Conjugative and Hyperconjugative Stabilization in Diynes, Dienes, and Related Compounds. Angew Chem Int Ed Engl 2005; 44:3617-20. [PMID: 15880719 DOI: 10.1002/anie.200500452] [Citation(s) in RCA: 87] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
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Steinke T, Cokoja M, Gemel C, Kempter A, Krapp A, Frenking G, Zenneck U, Fischer RA. C-H-aktivierte Isomere von [M(AlCp*)5] (M=Fe, Ru). Angew Chem Int Ed Engl 2005. [DOI: 10.1002/ange.200462834] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
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Steinke T, Cokoja M, Gemel C, Kempter A, Krapp A, Frenking G, Zenneck U, Fischer RA. CH Activated Isomers of [M(AlCp*)5] (M=Fe, Ru). Angew Chem Int Ed Engl 2005; 44:2943-6. [PMID: 15828045 DOI: 10.1002/anie.200462834] [Citation(s) in RCA: 64] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
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Lein M, Krapp A, Frenking G. Why Do the Heavy-Atom Analogues of Acetylene E2H2(E = Si−Pb) Exhibit Unusual Structures? J Am Chem Soc 2005; 127:6290-9. [PMID: 15853336 DOI: 10.1021/ja042295c] [Citation(s) in RCA: 151] [Impact Index Per Article: 7.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
DFT calculations at BP86/QZ4P have been carried out for different structures of E(2)H(2) (E = C, Si, Ge, Sn, Pb) with the goal to explain the unusual equilibrium geometries of the heavier group 14 homologues where E = Si-Pb. The global energy minima of the latter molecules have a nonplanar doubly bridged structure A followed by the singly bridged planar form B, the vinylidene-type structure C, and the trans-bent isomer D1. The energetically high-lying trans-bent structure D2 possessing an electron sextet at E and the linear form HEEH, which are not minima on the PES, have also been studied. The unusual structures of E(2)H(2) (E = Si-Pb) are explained with the interactions between the EH moieties in the (X(2)Pi) electronic ground state which differ from C(2)H(2), which is bound through interactions between CH in the a(4)Sigma(-) excited state. Bonding between two (X(2)Pi) fragments of the heavier EH hydrides is favored over the bonding in the a(4)Sigma(-) excited state because the X(2)Pi --> a(4)Sigma(-) excitation energy of EH (E = Si-Pb) is significantly higher than for CH. The doubly bridged structure A of E(2)H(2) has three bonding orbital contributions: one sigma bond and two E-H donor-acceptor bonds. The singly bridged isomer B also has three bonding orbital contributions: one pi bond, one E-H donor-acceptor bond, and one lone-pair donor-acceptor bond. The trans-bent form D1 has one pi bond and two lone-pair donor-acceptor bonds, while D2 has only one sigma bond. The strength of the stabilizing orbital contributions has been estimated with an energy decomposition analysis, which also gives the bonding contributions of the quasi-classical electrostatic interactions.
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Scheibitz M, Bolte M, Bats JW, Lerner HW, Nowik I, Herber RH, Krapp A, Lein M, Holthausen MC, Wagner M. C5H4?BR2 Bending in Ferrocenylboranes: A Delocalized Through-Space Interaction Between Iron and Boron. Chemistry 2005; 11:584-603. [PMID: 15580647 DOI: 10.1002/chem.200400690] [Citation(s) in RCA: 118] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Abstract
A comparison of the molecular structures of mono-, di- and tetraborylated ferrocenes [Fc{B(R(1))(R(2))}] (R(1)/R(2)=Br/Br, Br/Fc, Br/Me, Me/Me, Me/OH, OMe/OMe), 1,1'-[fc{B(R(1))(R(2))}(2)] (R(1)/R(2)=Br/Br, Br/Me, OMe/OMe), and 1,1',3,3'-[Fe{C(5)H(3)(BMe(2))(2)}(2)] revealed the boryl substituent(s) to be bent out of the Cp ring plane towards the iron center. The corresponding dip angle alpha* decreases with decreasing Lewis acidity of the boron atom and with increasing degree of borylation at the ferrocene core. This trend is well reproduced by DFT calculations (including [FcBH(2)], not yet accessible experimentally). A Bader analysis of the electron density topology of [FcBH(2)] (alpha*=26.5 degrees ; BP86/TZVP) clearly showed that there is no direct iron-boron bonding in this compound. Instead, strongly delocalized orbital interactions have been identified that involve the boron p orbital, C(ipso) of the adjacent Cp ring, d orbitals at iron, and a through-space interaction with the second Cp ring. A second important factor is attractive electrostatic interactions, which are enhanced upon ligand bending. Cyclic voltammetric measurements on the series [FcBMe(2)], 1,1'-[fc(BMe(2))(2)], and 1,1',3,3'-[Fe{C(5)H(3)(BMe(2))(2)}(2)] indicate a substantial anodic shift in the oxidation potential of the central iron atom upon introduction of BMe(2) substituents. Addition of 4-dimethylaminopyridine (DMAP) does not just counterbalance this effect, but leads to a cathodic shift of the Fe(II)/Fe(III) redox transition far beyond the half-wave potential of parent ferrocene. In the Mossbauer spectra, a continuous decrease in the quadrupole splitting (QS) is observed upon going from parent ferrocene to [FcBMe(2)], to 1,1'-[fc(BMe(2))(2)], and to 1,1',3,3'-[Fe{C(5)H(3)(BMe(2))(2)}(2)]. In contrast, no significant differences are found between the QS values of ferrocene, [Fc(BMe(2)-DMAP)], and 1,1'-[fc(BMe(2)-DMAP)(2)].
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Lewalter D, Krapp A. The Role of Contextual Conditions of Vocational Education for Motivational Orientations and Emotional Experiences. EUROPEAN PSYCHOLOGIST 2004. [DOI: 10.1027/1016-9040.9.4.210] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Abstract
This article is concerned with the role of contextual conditions on motivational orientations and emotional experiences within the German Dual System of vocational education (VE). In our research approach we differentiate between three exemplary levels and meanings of context: educational setting, learning arrangement, and learning situation. Prior research in Germany has focused primarily on the analyses of differential motivational conditions and effects in two main educational settings: vocational school and training in companies. In a study in the educational setting of a company we tried to analyze the relation among contextual aspects at the level of learning arrangements and learning situations, intrinsic and extrinsic motivational orientations, and a selected set of emotional experiences. We used a variety of different methodological approaches including video-based observations, and the experience-sampling method (ESM). Comparing the indicators of extrinsic and intrinsic motivational orientations between the two main learning arrangements (training at the workplace and lessons about vocational knowledge), we found significant differences only for interest orientation (not for achievement orientation) and for exemplary indicators of a positive emotional experiences (feelings of being interested and feelings of being committed). Contrary to our theoretical expectations, the measures indicating the quality of emotional experiences with respect to the postulated system of basic needs (competence, autonomy, relatedness) did not vary systematically with the contextual conditions under consideration.
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Krapp A. Beschreibung und Erklärung antagonistisch wirkender Steuerungssysteme in pädagogisch-psychologischen Motivationstheorien. ZEITSCHRIFT FUR PADAGOGISCHE PSYCHOLOGIE 2004. [DOI: 10.1024/1010-0652.18.34.145] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
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Krapp A, Schmidt S, Cano E, Simanis V. S. pombe cdc11p, together with sid4p, provides an anchor for septation initiation network proteins on the spindle pole body. Curr Biol 2001; 11:1559-68. [PMID: 11676915 DOI: 10.1016/s0960-9822(01)00478-x] [Citation(s) in RCA: 75] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
BACKGROUND The signal for the onset of septum formation in the fission yeast Schizosaccharomyces pombe is transduced by the septation initiation network (SIN). Many of the components of the SIN are located on the spindle pole body during mitosis, from where it is presumed that the signal for septum formation is delivered. Cdc11 mutants are defective in SIN signaling, but the role of cdc11 in the pathway has remained enigmatic. RESULTS We have cloned the cdc11 gene by a combination of chromosome walking and transfection of cosmids into a cdc11 mutant. Cdc11p most closely resembles Saccharomyces cerevisiae Nud1p and is essential for septum formation. Cdc11p is a phosphoprotein, which becomes hyperphosphorylated during anaphase. It localizes to the spindle pole body at all stages of the cell cycle, in a sid4p-dependent manner, and cdc11p is required for the localization of all the known SIN components, except sid4p, to the SPB. Cdc11p and sid4p can be coimmunoprecipitated from cell extracts. Finally, like its S. cerevisiae ortholog Nud1p, cdc11p is involved in the proper organization of astral microtubules during mitosis. CONCLUSIONS We propose that cdc11p acts as a bridge between sid4p and the other SIN proteins, mediating their association with the spindle pole body.
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Bogado I, Sutich E, Krapp A, Marchiaro P, Marzi M, Putero J, Carrillo N. Methicillin resistance study in clinical isolates of coagulase-negative staphylococci and determination of their susceptibility to alternative antimicrobial agents. J Appl Microbiol 2001; 91:344-50. [PMID: 11473600 DOI: 10.1046/j.1365-2672.2001.01400.x] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
AIMS To achieve reliable detection of methicillin resistance in clinical isolates of coagulase-negative staphylococci. METHODS AND RESULTS Strains (105) were evaluated by normatized antimicrobial susceptibility methods, and for the presence of the methicillin resistance-determining mecA gene, using the polymerase chain reaction. Correlation between phenotypic and genotypic methods was obtained in 87.6% of the samples. Six strains, classified as methicillin-susceptible by phenotypic assays, revealed the presence of the mecA gene, indicating that methicillin resistance expression was probably repressed. Another seven isolates failed to show mecA amplification after displaying methicillin resistance in phenotypic evaluations. The susceptibility of the methicillin-resistant isolates to other antimicrobial agents was variable. CONCLUSION Genotypic determination of the mecA gene proved to be the most reliable method for detection of methicillin resistance. SIGNIFICANCE AND IMPACT OF THE STUDY Correct assessment of methicillin resistance, such as that attained through genotyping, is essential for defining therapeutic strategies, particularly when treating severely compromised patients.
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Krapp A. Wie berechtigt ist die permanente Kritik an den vermeintlichen Unzulänglichkeiten der Pädagogischen Psychologie? ZEITSCHRIFT FUR PADAGOGISCHE PSYCHOLOGIE 2001. [DOI: 10.1024//1010-0652.15.2.71] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
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Krapp A, Strubin M. B-Cell coactivator OBF-1 exhibits unusual transcriptional properties and functions in a DNA-bound Oct-1-dependent fashion. Mol Cell Biol 1999; 19:4247-54. [PMID: 10330165 PMCID: PMC104384 DOI: 10.1128/mcb.19.6.4247] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Eukaryotic transcriptional activators generally comprise both a DNA-binding domain that recognizes specific cis-regulatory elements in the target genes and an activation domain which is essential for transcriptional stimulation. Activation domains typically behave as structurally and functionally autonomous modules that retain their intrinsic activities when directed to a promoter by a variety of heterologous DNA-binding domains. Here we report that OBF-1, a B-cell-specific coactivator for transcription factor Oct-1, challenges this traditional view in that it contains an atypical activation domain that exhibits two unexpected functional properties when tested in the yeast Saccharomyces cerevisiae. First, OBF-1 by itself has essentially no intrinsic activation potential, yet it strongly synergizes with other activation domains such as VP16 and Gal4. Second, OBF-1 exerts its effect in association with DNA-bound Oct-1 but is inactive when attached to a heterologous DNA-binding domain. These findings suggest that activation by OBF-1 is not obtained by simple recruitment of the coactivator to the promoter but requires interaction with DNA-bound Oct-1 to stimulate a step distinct from those regulated by classical activation domains.
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Krapp A, Knöfler M, Ledermann B, Bürki K, Berney C, Zoerkler N, Hagenbüchle O, Wellauer PK. The bHLH protein PTF1-p48 is essential for the formation of the exocrine and the correct spatial organization of the endocrine pancreas. Genes Dev 1998; 12:3752-63. [PMID: 9851981 PMCID: PMC317250 DOI: 10.1101/gad.12.23.3752] [Citation(s) in RCA: 425] [Impact Index Per Article: 16.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
We have generated a mouse bearing a null allele of the gene encoding basic helix-loop-helix (bHLH) protein p48, the cell-specific DNA-binding subunit of hetero-oligomeric transcription factor PTF1 that directs the expression of genes in the exocrine pancreas. The null mutation, which establishes a lethal condition shortly after birth, leads to a complete absence of exocrine pancreatic tissue and its specific products, indicating that p48 is required for differentiation and/or proliferation of the exocrine cell lineage. p48 is so far the only developmental regulator known to be required exclusively for committing cells to an exocrine fate. The hormone secreting cells of all four endocrine lineages are present in the mesentery that normally harbors the pancreatic organ until day 16 of gestation. Toward the end of embryonic life, cells expressing endocrine functions are no longer detected at their original location but are now found to colonize the spleen, where they persist in a functional state until postnatal death of the organism occurs. These findings suggest that the presence of the exocrine pancreas is required for the correct spatial assembly of the endocrine pancreas and that, in its absence, endocrine cells are directed by default to the spleen, a site that, in some reptiles, harbors part of this particular cellular compartment.
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Matt P, Schurr U, Klein D, Krapp A, Stitt M. Growth of tobacco in short-day conditions leads to high starch, low sugars, altered diurnal changes in the Nia transcript and low nitrate reductase activity, and inhibition of amino acid synthesis. PLANTA 1998; 207:27-41. [PMID: 9951717 DOI: 10.1007/s004250050452] [Citation(s) in RCA: 57] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/22/2023]
Abstract
Diurnal changes in carbohydrates and nitrate reductase (NR) activity were compared in tobacco (Nicotiana tabacum. L.cv. Gatersleben) plants growing in a long (18 h light/6 h dark) and a short (6 h light/18 h dark) day growth regime, or after short-term changes in the light regime. In long-day-grown plants, source leaves contained high levels of sugars throughout the light and dark periods. In short-day-grown plants, levels of sucrose and reducing sugars were very low at the end of the night and, although they rose during the light period, remained much lower than in long days and declined to very low levels again by the middle of the night. Starch accumulated more rapidly in short-day-than long-day-grown plants. Starch was completely remobilised during the night in short days, but not in long days. A single short day/long night cycle sufficed to stimulate starch accumulation during the following light period. In long-day-grown plants, the Nia transcript level was high at the end of the night, decreased during the day, and recovered gradually during the night. In short-day-grown plants, the Nia transcript level was relatively low at the end of the night, decreased to very low levels at the end of the light period, increased to a marked maximum in the middle of the night, and decreased during the last 5 h of the dark period. In long-day-grown plants, NR activity in source leaves rose by 2- to 3-fold in the first part of the light period and decreased in the second part of the light period. In short-day-grown plants, NR activity was low at the end of the night, and only increased slightly after illumination. Dark inactivation of source-leaf NR was partially reversed in long-day-grown plants, but not in short day-grown plants. In both growth regimes, mutants with one instead of four functional copies of the Nia gene had a 60% reduction in maximum NR activity in the source leaves, compared to wild-type plants. The diurnal changes in NR activity were almost completely suppressed in the mutants in long days, whereas the mutants showed similar or slightly larger diurnal changes than wild-type plants in short days. When short-day-grown plants were transferred to long-day conditions for 3 d, NR activity and the diurnal changes in NR activity resembled those in long-day-grown plants. Phloem export from source leaves of short-day-grown plants was partially inhibited by applying a cold-girdle for one light and dark cycle. The resulting increase in leaf sugar was accompanied by an marked increase in the Nia transcript level and a 2-fold increase in NR activity at the end of the dark period. When wild-type plants were subjected to a single short day/long night cycle of increasing severity, NR activity in source leaves at the end of the night decreased when the endogenous sugars declined below about 3 mumol hexose (g FW)-1. In sink leaves in short-day conditions, sugars were higher and the light-induced rise in NR activity was much larger than in source leaves on the same plants. The source leaves of wild-type plants in short-day conditions contained very high levels of nitrate, very low levels of glutamine, low levels of total amino acids, and lower protein and chlorophyll, compared to long-day-grown plants. Plants grown in short days had relatively high levels of glutamate and aspartate, and extremely low levels of most of the minor amino acids in their source leaves at the end of the night. Illumination led to a decrease in glutamate and an increase in the minor amino acids. A single short day/long night cycle led to an increase in glutamate, and a large decrease in the minor acids at the end of the dark period, and reillumination led to a decrease in glutamate and an increase in the minor amino acids. It is proposed that sugar-mediated control of Nia expression and NR activity overrides regulation by nitrogenous compounds when sugars are in short supply, resulting in a severe inhibition of nitrate assimilation. It is also proposed that su
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Quesada A, Krapp A, Trueman LJ, Daniel-Vedele F, Fernández E, Forde BG, Caboche M. PCR-identification of a Nicotiana plumbaginifolia cDNA homologous to the high-affinity nitrate transporters of the crnA family. PLANT MOLECULAR BIOLOGY 1997; 34:265-74. [PMID: 9207842 DOI: 10.1023/a:1005872816881] [Citation(s) in RCA: 25] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/09/2023]
Abstract
A family of high-affinity nitrate transporters has been identified in Aspergillus nidulans and Chlamydomonas reinhardtii, and recently homologues of this family have been cloned from a higher plant (barley). Based on six of the peptide sequences most strongly conserved between the barley and C. reinhardtii polypeptides, a set of degenerate primers was designed to permit amplification of the corresponding genes from other plant species. The utility of these primers was demonstrated by RT-PCR with cDNA made from poly(A)+ RNA from barley, C. reinhardtii and Nicotiana plumbaginifolia. A PCR fragment amplified from N. plumbaginifolia was used as probe to isolate a full-length cDNA clone which encodes a protein, NRT2;1Np, that is closely related to the previously isolated crnA homologue from barley. Genomic Southern blots indicated that there are only 1 or 2 members of the Nrt2 gene family in N. plumbaginifolia. Northern blotting showed that the Nrt2 transcripts are most strongly expressed in roots. The effects of external treatments with different N sources showed that the regulation of the Nrt2 gene(s) is very similar to that reported for nitrate reductase and nitrite reductase genes: their expression was strongly induced by nitrate but was repressed when reduced forms of N were supplied to the roots.
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Knöfler M, Krapp A, Hagenbüchle O, Wellauer PK. Constitutive expression of the gene for the cell-specific p48 DNA-binding subunit of pancreas transcription factor 1 in cultured cells is under control of binding sites for transcription factors Sp1 and alphaCbf. J Biol Chem 1996; 271:21993-2002. [PMID: 8703005 DOI: 10.1074/jbc.271.36.21993] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023] Open
Abstract
We have cloned and characterized the rat gene that encodes the p48 DNA-binding subunit of pancreas transcription factor 1 (Ptf1), a cell-specific basic region helix-loop-helix (bHLH) protein. The ptf1-p48 gene measures 1.8 kilobases in size and occurs as a single copy in the haploid genome. Run-on transcription assays suggest that this gene is subject to transcriptional control since no activity of its promoter is detected in nonproducing cells. The gene specifies two mRNAs that encode the same protein and originate from transcription initiation at alternative sites. Expression analysis of hybrid genes bearing deletions of the gene's 5'-flanking region fused to a reporter gene defines a promoter region within the gene-proximal 260 base pairs of DNA. The cis-acting elements that control promoter activity include binding sites for transcription factors Sp1 and alphaCbf, a 60-kDa CCAAT box-binding protein. The gene promoter, however, functions not only in exocrine pancreatic cells but also in cells of other origin. No cell-specific transcriptional control element was detected in as much as 10 kilobases of 5'-flanking region. We discuss models of how the cell-specific expression of the endogenous ptf1-p48 gene might be established during development of the animal.
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Krapp A, Knöfler M, Frutiger S, Hughes GJ, Hagenbüchle O, Wellauer PK. The p48 DNA-binding subunit of transcription factor PTF1 is a new exocrine pancreas-specific basic helix-loop-helix protein. EMBO J 1996. [DOI: 10.1002/j.1460-2075.1996.tb00806.x] [Citation(s) in RCA: 183] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022] Open
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Krapp A, Knöfler M, Frutiger S, Hughes GJ, Hagenbüchle O, Wellauer PK. The p48 DNA-binding subunit of transcription factor PTF1 is a new exocrine pancreas-specific basic helix-loop-helix protein. EMBO J 1996; 15:4317-29. [PMID: 8861960 PMCID: PMC452157] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023] Open
Abstract
We report the isolation of cDNA for the p48 DNA-binding subunit of the heterooligomeric transcription factor PTF1. A sequence analysis of the cDNA demonstrates that p48 is a new member of the family of basic helix-loop-helix (bHLH) transcription factors. The p48 bHLH domain shows striking amino acid sequence similarity with the bHLH domain of proteins that act as developmental regulators, including the twist gene product, myogenic factors and proteins involved in hematopoietic differentiation. We show that reduced p48 synthesis correlates with a diminished expression of genes encoding exocrine pancreas-specific functions. The synthesis of p48 mRNAs, and therefore also the protein, is restricted to cells of the exocrine pancreas in the adult and to the pancreatic primordium in the embryo. Thus the pancreas-specific DNA-binding activity of PTF1 originates from the synthesis of at least one cell-specific component rather than from a cell-specific assembly of more widely distributed proteins.
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Beisiegel U, Krapp A, Weber W, Olivecrona G, Gliemann J. The role of lipases and LRP in the catabolism of triglyceride-rich lipoproteins. ZEITSCHRIFT FUR GASTROENTEROLOGIE 1996; 34 Suppl 3:108-9. [PMID: 8767481] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
A strong candidate for the long searched CR receptor might be the a2MR/LRP. We oversee a whole series of in vitro experiments from different laboratories today which show that LRP expresses all features for being such a receptor protein. LRP is localized on the liver cell surface, as well as on most other animal cells. It recognizes apo E enriched lipoproteins, as beta-VLDL and CR. There is evidence that CR contains LPL and it has been demonstrated that LPL binds with high affinity to LRP. This has been shown in cell binding experiments with subsequent cross-linking and in direct binding assays on purified receptor protein. HL which is expressed in liver cells and localized at the liver cell surface is also able to bind to LRP. LRP is moreover found in endosomes and can mediate the uptake of beta-VLDL and CR. Further studies are necessary to evaluate its role in vivo as well as its regulation. The interplay between the different ligands of this large multifunctional receptor protein needs to be clarified. It should be emphasized here that by describing LPL as a new mediator of CR untake in the liver and providing evidence for an interaction between LPL and LRP the role of LRP in the remnant catabolism has become even more likely.
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Krapp A, Ahle S, Kersting S, Hua Y, Kneser K, Nielsen M, Gliemann J, Beisiegel U. Hepatic lipase mediates the uptake of chylomicrons and beta-VLDL into cells via the LDL receptor-related protein (LRP). J Lipid Res 1996; 37:926-36. [PMID: 8725146] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023] Open
Abstract
The uptake of triglyceride-rich lipoproteins has been described as being mediated by apolipoprotein E and lipoprotein lipase (LpL). Proteoglycans, the LDL-receptor, and the LDL receptor-related protein (LRP) are the cellular acceptors. In addition to LpL, hepatic lipase (HL) has been shown to bind to LRP. In this study, the role of HL in lipoprotein uptake was investigated. Human chylomicrons and rabbit beta-VLDL were used as ligands for human hepatoma cells, primary human hepalocytes, normal and proteoglycan-deficient Chinese hamster ovary (CHO) cells, and normal and LDL receptor-deficient human fibroblasts. We show that HL induces stimulation of the uptake of chylomicrons and beta-VLDL into the different cell lines. HL is known to bind to heparan sulfate, and experiments on normal and proteoglycan-deficient CHO cells showed that cell surface proteoglycans are essential for HL-mediated uptake of lipoproteins. To exclude LDL receptor-mediated uptake. we performed experiments on LDL receptor-deficient fibroblasts that demonstrated that the LDL receptor was not important for the HL-mediated uptake of lipoproteins. Crosslinking experiments confirmed the binding of HL to LRP on the cell surface. To identify the region of HL involved in the interaction with LRP, we used a C-terminal fragment of LpL, known to inhibit LpL-mediated uptake. HL-mediated lipoprotein uptake was suppressed by this fragment. Our experiments indicate that HL, like LpL, can mediate the uptake of lipoproteins into cells, most probably via a C-terminal binding site. The uptake, initiated by proteoglycan binding, is mediated by LRP.
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Godon C, Krapp A, Leydecker MT, Daniel-Vedele F, Caboche M. Methylammonium-resistant mutants of Nicotiana plumbaginifolia are affected in nitrate transport. MOLECULAR & GENERAL GENETICS : MGG 1996; 250:357-66. [PMID: 8602151 DOI: 10.1007/bf02174394] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
This work reports the isolation and preliminary characterization of Nicotiana plumbaginifolia mutants resistant to methylammonium. Nicotiana plumbaginifolia plants cannot grow on low levels of nitrate in the presence of methylammonium. Methylammonium is not used as a nitrogen source, although it can be efficiently taken up by Nicotiana plumbaginifolia cells and converted into methylglutamine, an analog of glutamine. Glutamine is known to repress the expression of the enzymes that mediate the first two steps in the nitrate assimilatory pathway, nitrate reductase (NR) and nitrite reductase (NiR). Methylammonium has therefore been used, in combination with low concentrations of nitrate, as a selective agent in order to screen for mutants in which the nitrate pathway is de-repressed. Eleven semi-dominant mutants, all belonging to the same complementation group, were identified. The mutant showing the highest resistance to methylammonium was not affected either in the utilization of ammonium, accumulation of methylammonium or in glutamine synthase activity. A series of experiments showed that utilization of nitrite by the wild-type and the mutant was comparable, in the presence or the absence of methylammonium, thus suggesting that the mutation specifically affected nitrate transport or reduction. Although NR mRNA levels were less repressed by methylammonium treatment of the wild-type than the mutant, NR activities of the mutant remained comparable with or without methylammonium, leading to the hypothesis that modified expression of NR is probably not responsible for resistance to methylammonium. Methylammonium inhibited nitrate uptake in the wild-type but had only a limited effect in the mutant. The implications of these results are discussed.
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