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H Bujard

Publications and source records attributed to H Bujard.

At least 37 records · Page 2Linked to original sources
PubMed1998

Doxycycline control of prion protein transgene expression modulates prion disease in mice.

Conversion of the cellular prion protein (PrPC) into the pathogenic isoform (PrPSc) is the fundamental event underlying transmission and pathogenesis of prion diseases. To control the expression of PrPC in transgenic (Tg) mice, we used a tetracycline controlled transactivator (tTA) driven by the PrP gene control elements and a tTA-responsive promoter linked to a PrP gene [Gossen, M. and Bujard, H. (1992) Proc. Natl. Acad. Sci. USA 89, 5547-5551]. Adult Tg mice showed no deleterious effects upon repression of PrPC expression (>90%) by oral doxycycline, but the mice developed progressive ataxia at approximately 50 days after inoculation with prions unless maintained on doxycycline. Although Tg mice on doxycycline accumulated low levels of PrPSc, they showed no neurologic dysfunction, indicating that low levels of PrPSc can be tolerated. Use of the tTA system to control PrP expression allowed production of Tg mice with high levels of PrP that otherwise cause many embryonic and neonatal deaths. Measurement of PrPSc clearance in Tg mice should be possible, facilitating the development of pharmacotherapeutics.

Animals↗
PubMed1997

Tetracycline-controlled transcription in eukaryotes: novel transactivators with graded transactivation potential.

Several tetracycline-controlled transactivators (tTA) were generated which differ in their activation potential by >3 orders of magnitude. The transactivators are fusions between the Tet repressor and minimal transcriptional activation domains derived from Herpes simplex virus protein 16 (VP16). By reducing the VP16 moiety of the previously described tTA to 12 amino acids, potential targets for interactions with various cellular transcription factors were eliminated, as were potential epitopes which may elicit a cellular immune response. When compared with the originally described tTA, these new transactivators are tolerated at higher intracellular concentrations. This will facilitate establishment of tet regulatory systems under a variety of conditions, but particularly when cell type-restricted tetracycline-controlled gene expression is to be achieved in transgenic organisms via homologous recombination.

Bacterial Proteins↗
PubMed1997

Independent and tight regulation of transcriptional units in Escherichia coli via the LacR/O, the TetR/O and AraC/I1-I2 regulatory elements.

Based on parameters governing promoter activity and using regulatory elements of the lac, ara and tet operon transcription control sequences were composed which permit the regulation in Escherichia coli of several gene activities independently and quantitatively. The novel promoter PLtetO-1 allows the regulation of gene expression over an up to 5000-fold range with anhydrotetracycline (aTc) whereas with IPTG and arabinose the activity of Plac/ara-1 may be controlled 1800-fold. Escherichia coli host strains which produce defined amounts of the regulatory proteins, Lac and Tet repressor as well as AraC from chromosomally located expression units provide highly reproducible in vivo conditions. Controlling the expression of the genes encoding luciferase, the low abundance E.coli protein DnaJ and restriction endonuclease Cfr9I not only demonstrates that high levels of expression can be achieved but also suggests that under conditions of optimal repression only around one mRNA every 3rd generation is produced. This potential of quantitative control will open up new approaches in the study of gene function in vivo, in particular with low abundance regulatory gene products. The system will also provide new opportunities for the controlled expression of heterologous genes.

Arabinose↗
PubMed1997

Epitope analysis of human T-cell response to MSP-1 of Plasmodium falciparum in malaria-nonexposed individuals.

BACKGROUND: MSP-1 of Plasmodium falciparum induces strong proliferative T cell responses even in malaria-nonexposed individuals. Epitopes recognized by malaria-nonimmune T cells have not been identified, and immunological mechanisms inducing such T cell responses remain to be uncovered. MSP-1 is a vaccine candidate, and it should be understood whether those epitopes have any roles in MSP-1-mediated protective immunity. The T epitopes-inducing malaria-naive T cell response was analyzed in the hope of understanding the underlying mechanisms. METHODS: Human T cell lines and clones reactive to MSP-1 of P. falciparum were established from malaria-nonexposed Japanese donors in vitro, and epitope peptides were identified. Sequences of those epitope peptides were compared to unrelated peptides in the data base. One of those peptides was tested for both binding to HLA-DR molecules and inducing proliferative responses of MSP-1-reactive T cells. RESULTS: There are at least 6 epitopes recognized by malaria-naive T cells under the restriction by HLA-DRB1*1502 or 0802. Important amino acids for the T cell recognition were identified for an MSP-1 peptide. A yeast peptide which shared those residues induced proliferative responses of MSP-1-reactive T cells. CONCLUSION: We identified T epitopes in the N-terminal region of MSP-1, some of which showed molecular similarities with unrelated environmental antigens, suggesting the presence of cross-reactive T epitopes in MSP-1. Cytokine production in response to those epitopes suggests regulatory functions of those T cells during primary infection with P. falciparum.

Amino Acid Sequence↗
PubMed1996

Doxycycline-mediated quantitative and tissue-specific control of gene expression in transgenic mice.

The tet regulatory system in which doxycycline (dox) acts as an inducer of specifically engineered RNA polymerase II promoters was transferred into transgenic mice. Tight control and a broad range of regulation spanning up to five orders of magnitude were monitored dependent on the dox concentration in the water supply of the animals. Administration of dox rapidly induces the synthesis of the indicator enzyme luciferase whose activity rises over several orders of magnitude within the first 4 h in some organs. Induction is complete after 24 h in most organs analyzed. A comparable regulatory potential was revealed with the tet regulatory system where dox prevents transcription activation. Directing the synthesis of the tetracycline-controlled transactivator (tTA) to the liver led to highly specific regulation in hepatocytes where, in presence of dox, less than one molecule of luciferase was detected per cell. By contrast, a more than 10(5)-fold activation of the luciferase gene was observed in the absence of the antibiotic. This regulation was homogeneous throughout but stringently restricted to hepatocytes. These results demonstrate that both tetracycline-controlled transcriptional activation systems provide genetic switches that permit the quantitative control of gene activities in transgenic mice in a tissue-specific manner and, thus, suggest possibilities for the generation of a novel type of conditional mutants.

Animals↗
PubMed1996

A cycle of binding and release of the DnaK, DnaJ and GrpE chaperones regulates activity of the Escherichia coli heat shock transcription factor sigma32.

The chaperone system formed by DnaK, DnaJ and GrpE mediates stress-dependent negative modulation of the Escherichia coli heat shock response, probably through association with the heat shock promoter-specific sigma32 subunit of RNA polymerase. Interactions of the DnaK system with sigma32 were analysed. DnaJ and DnaK bind free, but not RNA polymerase-bound, sigma32 with dissociation constants of 20 nM and 5 muM respectively. Association and dissociation rates of DnaJ-sigma32 complexes are 5900- and 20-fold higher respectively than those of DnaK-sigma32 complexes in the absence of ATP. ATP destabilizes DnaK-sigma32 interactions. DnaJ, through rapid association with sigma32 and stimulation of hydrolysis of DnaK-bound ATP, mediates efficient binding of DnaK to sigma32 in the presence of ATP, resulting in DnaK-DnaJ-sigma32 complexes containing ADP. GrpE binding to these complexes stimulates nucleotide release and subsequent complex dissociation by ATP. We propose that the principles of this cycle also operate in other chaperone activities of the DnaK system. DnaK and DnaJ cooperatively inhibit sigma32 activity in heat shock gene transcription and GrpE partially reverses this inhibition. These data indicate that reversible inhibition of sigma32 activity through transient association of DnaK and DnaJ is a central regulatory element of the heat shock response.

Adenosine Diphosphate↗
PubMed1995

Transcriptional activation by tetracyclines in mammalian cells.

A transcriptional transactivator was developed that fuses the VP16 activation domain with a mutant Tet repressor from Escherichia coli. This transactivator requires certain tetracycline (Tc) derivatives for specific DNA binding. Thus, addition of doxycycline to HeLa cells that constitutively synthesized the transactivator and that contained an appropriate, stably integrated reporter unit rapidly induced gene expression more than a thousandfold. The specificity of the Tet repressor-operator-effector interaction and the pharmacological characteristics of Tc's make this regulatory system well suited for the control of gene activities in vivo, such as in transgenic animals and possibly in gene therapy.

Amino Acid Sequence↗
PubMed1995

Plasmodium falciparum: variations within the C-terminal region of merozoite surface antigen-1.

Sequence variations at the 3'-end of the Plasmodium falciparum merozoite surface antigen-1 gene show that the C-terminus of the protein may not be as conserved as has been assumed in the past. We have therefore examined the sequences of the 3' terminal 2 kb, i.e., blocks 12-17 of four isolates, RO-33, RO-71, 3D7A, and FCH5. We discuss different mechanisms of genetic exchange that could account for the observed variations. Furthermore the deduced amino acid sequences allow us to identify allelic epitopes of three monoclonal antibodies. Finally, our data complete the sequence of two additional independent alleles of this gene (RO-33 and RO-71).

Animals↗
PubMed1995

Tetracycline-regulated gene expression following direct gene transfer into mouse skeletal muscle.

For most experimental and therapeutic applications of gene transfer, regulation of the timing and level of gene expression is preferable to constitutive gene expression. Among the systems that have been developed for pharmacologically controlled gene expression in mammalian cells, the bacterial tetracycline (tet)-responsive system has the advantage that it is dependent on a drug (tet) that is both highly specific and non-toxic. The tet-responsive system has been previously used to modulate expression of cell cycle regulatory proteins in cultured cells, reporter genes in plants and transgenic mice and reporter genes directly injected into the heart. Here we show that orally or parenterally administered tet regulates expression of tet-responsive plasmids injected directly into mouse skeletal muscle. Reporter gene expression was suppressed by two orders of magnitude in the presence of tet, and that suppression was reversed when tet was withdrawn. These data show that skeletal muscle offers an accessible and well characterized target tissue for tet-controlled expression of genes in vivo, suggesting applications to developmental studies and gene therapy.

Animals↗
PubMed1994

Temporal control of gene expression in transgenic mice by a tetracycline-responsive promoter.

Promoters whose temporal activity can be directly manipulated in transgenic animals provide a tool for the study of gene functions in vivo. We have evaluated a tetracycline-responsive binary system for its ability to temporally control gene expression in transgenic mice. In this system, a tetracycline-controlled trans-activator protein (tTA), composed of the repressor of the tetracycline-resistance operon (tet from Escherichia coli transposon Tn10) and the activating domain of viral protein VP16 of herpes simplex virus, induces transcription from a minimal promoter (PhCMV*-1; see below) fused to seven tet operator sequences in the absence of tetracycline but not in its presence. Transgenic mice were generated that carried either a luciferase or a beta-galactosidase reporter gene under the control of PhCMV*-1 or a transgene containing the tTA coding sequence under the control of the human cytomegalovirus immediate early gene 1 (hCMV IE1) promoter/enhancer. Whereas little luciferase or beta-galactosidase activity was observed in tissues of mice carrying only the reporter genes, the presence of tTA in double-transgenic mice induced expression of the reporter genes up to several thousand-fold. This induction was abrogated to basal levels upon administration of tetracycline. These findings can be used, for example, to design dominant gain-of-function experiments in which temporal control of transgene expression is required.

Animals↗
PubMed1994

Displacement of housekeeping proteasome subunits by MHC-encoded LMPs: a newly discovered mechanism for modulating the multicatalytic proteinase complex.

The degradation of cytoplasmic antigens to peptides presented by class I MHC molecules is thought to be mediated by the ubiquitin/proteasome pathway. Support for this view came from our observation that the subunit composition of proteasomes can be changed by interferon-gamma (IFN-gamma) treatment. Thereby two subunits, LMP2 and LMP7, which are encoded in the MHC class II region, are incorporated into the proteasomal complex, whereas other subunits disappear. In the experiments reported in this communication we studied the subunit changes occurring in cell lines where the expression of LMP2 or LMP7 can be regulated individually either by IFN-gamma induction or by applying a new system to control the expression of transfected LMPs. In both situations LMP2 induction leads exclusively to the disappearance of housekeeping subunit 2, whereas LMP7 affects only subunit 10. Subunit 2 was found to be 76% homologous to LMP2. Since incorporation of LMP2 into the proteasomal complex prevents processing of the subunit 2 precursor, we conclude that LMP2 displaces subunit 2 during assembly. Subunit displacement is most likely a general mechanism to modulate the catalytic activity of the proteasomal complex without changing its structure. Furthermore, the controlled incorporation of transfected subunits into the complex offers a new approach to study proteasome function in vivo.

Amino Acid Sequence↗
PubMed1994

Stalling of Escherichia coli RNA polymerase in the +6 to +12 region in vivo is associated with tight binding to consensus promoter elements.

Three synthetic promoters, PS1, PS2 and PS3, which differ in their core promoter elements, were studied in vivo and in vitro. Whereas an increased homology score correlates with higher rates of RNA polymerase binding, it does not correlate with activity in vivo. Permanganate probing in vivo reveals that PS1, which exhibits the lowest homology score, is rate-limited during the early phase of promoter-RNA polymerase interactions. By contrast, PS2 and PS3, with higher homology scores, are limited at a late step involving an open DNA region spanning from +6 to +12, indicating a stalling of RNA polymerase. These complexes disappear upon treatment of cells with rifampicin and are replaced by open complexes covering the start site. Because initiated complexes are selectively insensitive to rifampicin action, this confirms that RNA polymerase stalled at +6 to +12 has initiated RNA synthesis. Kinetic studies indicate that the enzyme is released slowly from this position and that this slow release appears to be responsible for the low promoter activity. For PS3, which exhibits the highest homology score and which binds RNA polymerase most efficiently, the release of the stalled complex is particularly slow. PS3 is found to be the weakest of the three promoters in vivo. These results support models in which promoter activity can be determined by various rate limiting steps, including those following the formation of open complexes and even the initiation of RNA synthesis.

Base Sequence↗