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  • 1
    ISSN: 1432-0843
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary We have developed a simple sensitive fluorometric assay for the measurement of total Bisantrene in plasma, red blood cells, and tissues to facilitate preclinical and clinical pharmacologic assessment of this active anticancer agent. The assay was used to measure the plasma disappearance and tissue concentrations of Bisantrene in the rabbit. Results are comparable to those reported with HPLC assays and with measurement of radioactivity in combusted tissue following IV administration of radiolabeled Bisantrene. We demonstrated that when a plasma concentration of approximately 50 μg/ml is not exceeded, Bisantrene remains in solution at that concentration. If Bisantrene is introduced into plasma at a concentration exceeding 50 μg/ml, precipitation of the drug is initiated and continues until the plasma concentration is no greater than 15 μg/ml. This finding supports our previous recommendation that in clinical trials Bisantrene should be administered at low concentrations over prolonged periods of time to maximize the bioavailability of the drug by minimizing precipitation of the drug in plasma.
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  • 2
    Electronic Resource
    Electronic Resource
    [s.l.] : Nature Publishing Group
    Nature 326 (1987), S. 822-822 
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] SIR-The question of whether authors should use the word 'first' to imply a priority research finding has received considerable comment in Nature recently12. It is of course demanding for a referee or editor to be vigilant and review the associated literature to ensure that such statements are ...
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  • 3
    ISSN: 1617-4623
    Keywords: Transcriptional Activation ; Upstream sequences
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The upstream activator sequence (UAS) found in Klebsiella pneumoniae nif promoters and required for the activation of transcription by nifA, is absent from the nifF-nifL intergenic region, but is present downstream from the nifLA transcription start at+59. To determine whether nif upstream activator sequences can function in a 3′ position, the nifH UAS was cloned downstream from the NifH transcription start, but no activation of transcription by nifA dependent upon the UAS in its 3′ location could be detected. A mild repressive effect was detectable when the nifH UAS was placed downstream of the nifH promoter, but not when the cat promoter was substituted for the nifLA promoter upstream from the motif at+59 described above. However, deletion analysis showed that the UAS motif located downstream of the nifLA promoter has a role in transcription from the nifF promoter, although it is situated at position-263 with respect to the nifF transcription start, about 100 bp further upstream than previously described occurrences of the activator sequence.
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  • 4
    ISSN: 1617-4623
    Keywords: Multicopy inhibition ; Transcription termination
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Certain multicopy plasmids bearing promoter sequences of nitrogen fixation (nif) genes inhibit expression of chromosomal genes in Nif+ Klebsiella pneumoniae, hence leading to a Nif- phenotype. This ‘multicopy inhibition’ has been attributed to the titration of the nif-specific activator protein NifA by the plasmid-borne promoter sequences. We now report that multicopy inhibition by nifH translational fusions is sensitive to frameshifts close to the nifH promoter. Transcriptional nifH fusion plasmids in which translation terminated near the nifH promoter were transcriptionally active and showed multicopy inhibition; introduction of a transcription terminator after the nifH coding sequence in these plasmids prevented their multicopy inhibition. Therefore it seems likely that premature termination of transcription prevents multicopy inhibition by the nifH promoter.
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  • 5
    Electronic Resource
    Electronic Resource
    [s.l.] : Nature Publishing Group
    Nature 358 (1992), S. 422-422 
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] The promoter sequence recognized by the holoenzyme (Ecr54) is generally characterized by the presence of GG and GC doublets 24 and 12 base pairs, respectively, upstream of the transcription initiation point (Table 1; refs 1,3), and activation requires binding of the appropriate activator protein ...
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  • 6
    Electronic Resource
    Electronic Resource
    [s.l.] : Nature Publishing Group
    Nature 320 (1986), S. 374-378 
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Deletion of nucleotides -72 to -184 in the K. pneumoniae nifH promoter greatly reduces its transcriptional activation by the m/-specific activator nif A (ref. 4), and relieves the inhibition of chromosomal m/gene expression2 usually shown by multiple copies of the nifH promoter5. We have analysed ...
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  • 7
    ISSN: 1399-0047
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: The X-ray crystal structure of d(TGCGCA)2 has been determined at 120 K to a resolution of 1.3 Å. Hexamer duplexes, in the Z-DNA conformation, pack in an arrangement similar to the `pure spermine form' [Egli et al. (1991). Biochemistry, 30, 11388–11402] but with significantly different cell dimensions. The phosphate backbone exists in two equally populated discrete conformations at one nucleotide step, around phosphate 11. The structure contains two ordered cobalt hexammine molecules which have roles in stabilization of both the Z-DNA conformation of the duplex and in crystal packing. A comparison of d(TGCGCA)2 with other Z-DNA hexamer structures available in the Nucleic Acid Database illustrates the elusive nature of crystal packing. A review of the interactions with the metal cations Na+, Mg2+ and Co3+ reveals a relatively small proportion of phosphate binding and that close contacts between metal ions are common. A prediction of the water structure is compared with the observed pattern in the reported structure.
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  • 8
    ISSN: 1574-6968
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Abstract To analyze regulation of the vanadium-dependent nitrogenase of Azotobacter vinelandii, plasmids carrying vnfE-, vnfH-, or vnfD-lacZ fusions were transferred to Escherichia coli. These genes were expressed only if VnfA was present. Deletions of the vnfE upstream region were constructed and comparison of a region necessary for expression with sequences upstream of other vnf genes indicated a substantially conserved motif, GTAC-N6-GTAC, hypothesized to be the binding site for VnfA. This motif was duplicated with 17 or 18 bases lying between each in the vnfH and vnfD promoters. Deletion analysis of the vnfH promoter indicated that both motifs were necessary for full expression. In footprinting experiments, VnfA significantly protected from methylation the guanine residues within or immediately adjacent to the proposed VnfA recognition motifs. The active form of VnfA is probably interacting dimers, a tetramer, or a higher order oligomer since two regions of dyad symmetry are required for its interaction with the DNA.
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  • 9
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    FEMS microbiology letters 61 (1989), S. 0 
    ISSN: 1574-6968
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Abstract The Desulfovibrio gigas nifH gene has been cloned and sequenced. It consists of an open-reading frame of 822 base pairs encoding a 274 amino acid polypeptide. A potential ntrA-dependent promotor sequence is present. The gene lacks an upstream activator sequence homologous to those often found in nif genes subject to activation by nifA.
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  • 10
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: σN (σ54) RNA polymerase holoenzyme closed complexes isomerize to open complexes in a reaction requiring nucleoside triphosphate hydrolysis by enhancer binding activator proteins. Here, we characterize Klebsiella pneumoniaeσN mutants, altered in the carboxy DNA-binding domain (F354A/F355A, F402A, F403A and F402A/F403A), that fail in activator-dependent transcription. The mutant holoenzymes have altered activator-dependent interactions with promoter sequences that normally become melted. Activator-dependent stable complexes accumulated slowly in vitro (F402A) and to a reduced final level (F403A, F402A/F403A, F354A/F355A). Similar results were obtained in an assay of activator-independent stable complex formation. Premelted templates did not rescue the mutants for stable preinitiation complex formation but did for deleted region I σN, suggesting different defects. The DNA-binding domain substitutions are within σN sequences previously shown to be buried upon formation of the wild-type holoenzyme or closed complex, suggesting that, in the mutants, alteration of the σN–core and σN–DNA interfaces has occurred to change holoenzyme activity. Core-binding assays with the mutant sigmas support this view. Interestingly, an internal deletion form of σN lacking the major core binding determinant was able to assemble into holoenzyme and, although unable to support activator-dependent transcription, formed a stable activator-independent holoenzyme promoter complex on premelted DNA templates.
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