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  • 1
    Electronic Resource
    Electronic Resource
    ExbB acts as a chaperone-like protein to stabilize TonB in the cytoplasm (1993)
    Oxford, UK : Blackwell Publishing Ltd
    Molecular microbiology 8 (1993), S. 0 
    Details
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: The TonB protein is required to transduce energy from the cytoplasmic membrane to outer membrane transport proteins of Gram-negative bacteria. Two accessory proteins, ExbB and ExbD, are required for TonB function and it has been suggested that TonB and ExbBD form a complex in the membrane. In this paper we demonstrate that there are two spatially distinct, functional interactions between ExbBD and TonB. First, there is an interaction between ExbBD and the N-terminal signal-like peptide of TonB, probabiy the formation of a stable complex in the membrane. Second, ExbB interacts with TonB in the cytoplasm. This interaction involves the domain of TonB that is normally periplasmic. Thus, this is a transient interaction which occurs during the synthesis and/or localization of TonB, implying a chaperone-like role for ExbB. The transmembrane topology of ExbB was shown to be consistent with this role.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-2958.1993.tb01582.x
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  • 2
    Electronic Resource
    Electronic Resource
    Polyphosphate kinase is a component of the Escherichia coli RNA degradosome (1997)
    Oxford, UK : Blackwell Science Ltd
    Molecular microbiology 26 (1997), S. 0 
    Details
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: The Escherichia coli degradosome is a multienzyme complex with four major protein components: the endoribonuclease RNase E, the exoribonuclease PNPase, the RNA helicase RhlB and enolase. The first three of these proteins are known to have important functions in mRNA processing and degradation. In this work, we identify an additional component of the degradosome, polyphosphate kinase (PPK), which catalyses the reversible polymerization of the γ-phosphate of ATP into polyphosphate (poly(P)). An E. coli strain deleted for the ppk gene showed increased stability of the ompA mRNA. Purified His-tagged PPK was shown to bind RNA, and RNA binding was prevented by hydrolysable ATP. Chemical modification of RNA by PPK, for example the addition or removal of 3′ or 5′ terminal phosphates, could not be detected. However, polyphosphate was found to inhibit RNA degradation by the degradosome in vitro. This inhibition was overcome by the addition of ADP, required for the degradation of polyphosphate and for the regeneration of ATP by PPK in the degradosome. Thus, PPK in the degradosome appears to maintain an appropriate microenvironment, removing inhibitory polyphosphate and NDPs and regenerating ATP.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2958.1997.5901947.x
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  • 3
    Electronic Resource
    Electronic Resource
    The Escherichia coli ATP-binding cassette (ABC) proteins (1998)
    Oxford BSL : Blackwell Science Ltd, UK
    Molecular microbiology 28 (1998), S. 0 
    Details
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: The recent completion of the Escherichia coli genome sequence (Blattner et al., 1997) has permitted an analysis of the complement of genomically encoded ATP-binding cassette (ABC) proteins. A total of 79 ABC proteins makes this the largest paralogous family of proteins in E. coli. These 79 proteins include 97 ABC domains (as some proteins include more than one ABC domain) and are components of 69 independent functional systems (as many systems involve more than one ABC domain). The ABC domains are often, but not exclusively, the energy-generating domains of multicomponent membrane-bound transporters. Thus, 57 of the 69 systems are ABC transporters, of which 44 are periplasmic-binding protein-dependent uptake systems and 13 are presumed exporters. The genes encoding these ABC transporters occupy almost 5% of the genome. Of the 12 systems that are not obviously transport related, the function of only one, the excision repair protein UvrA, is known. A phylogenetic analysis suggests that the majority of ABC proteins can be assigned to 10 subfamilies. Together with statistical and, importantly, biological evidence, this analysis provides insight into the evolution and function of the ABC proteins.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2958.1998.00764.x
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  • 4
    Electronic Resource
    Electronic Resource
    Escherichia coli endoribonuclease RNase E: autoregulation of expression and site-specific cleavage of mRNA (1993)
    Oxford, UK : Blackwell Publishing Ltd
    Molecular microbiology 9 (1993), S. 0 
    Details
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: Mutations in the Escherichia coli rne (ams) gene have a general effect on the rate of mRNA decay in vivo. Using antibodies we have shown that the product of the rne gene is a polypeptide of relative mobility 180kDa. However, proteolytic fragments as small as 70kDa, which can arise during purification, also exhibit RNase E activity, in vitro studies demonstrate that the rne gene product, RNase E, is an endoribonuclease that cleaves mRNA at specific sites. RNase E cleaves rne mRNA and autoregulates the expression of the rne gene. In addition we demonstrate RNase E-dependent endonucleolytic cleavage of ompA mRNA, at a site known to be rate-determining for degradation and reported to be cieaved by RNase K. Our data are consistent with RNase K being a proteolytic fragment of RNase E.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-2958.1993.tb01716.x
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  • 5
    Electronic Resource
    Electronic Resource
    Multiple molecular mechanisms for multidrug resistance transporters (2007)
    [s.l.] : Nature Publishing Group
    Nature 446 (2007), S. 749-757 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] The acquisition of multidrug resistance is a serious impediment to improved healthcare. Multidrug resistance is most frequently due to active transporters that pump a broad spectrum of chemically distinct, cytotoxic molecules out of cells, including antibiotics, antimalarials, herbicides and ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/nature05630
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  • 6
    Electronic Resource
    Electronic Resource
    Localized domains of DNA supercoiling: topological coupling between promoters (1996)
    Oxford BSL : Blackwell Science Ltd
    Molecular microbiology 22 (1996), S. 0 
    Details
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: According to the twin-supercoiled domain model, a local domain with a high level of DNA supercoiling can be generated between two divergently transcribed promoters. We have tested this model directly using the rate of DNA photo-cross-linking by 4,5′,8-trimethylpsoralen to measure local regions of unconstrained supercoiling in vivo. We demonstrate that, in plasmids, a localized domain of highly supercoiled DNA is generated upstream of the tetA promoter. The level of supercoiling of this domain depends on the activity of the tetA promoter and on the extent of translation of the tetA gene product. The highest level of supercoiling within this localized domain was observed in a topA strain, although the generation of a localized supercoiling domain could also be detected in a topA+ background, consistent with potential physiological significance. The level of supercoiling in this localized domain correlated with activation of the supercoiling-sensitive leu-500 promoter located upstream of tetA. These data provide a direct demonstration that localized domains of increased negative supercoiling can be generated upstream of an actively transcribed promoter, and that this can result in supercoiling-mediated transcriptional coupling between two promoters.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2958.1996.01541.x
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  • 7
    Electronic Resource
    Electronic Resource
    Expression and mutational analysis of the nucleoid-associated protein H-NS of Salmonella typhimurium (1992)
    Oxford, UK : Blackwell Publishing Ltd
    Molecular microbiology 6 (1992), S. 0 
    Details
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: The H-NS (H1) protein is a major component of bacterial chromatin. Mutations in the hns (osmZ) gene encoding H-NS are highly pleiotropic, affecting the expression of many unrelated genes in an allele-specific manner. H-NS expression was found not to vary with growth phase or growth medium osmolarity. Additionally, 10 independent hns mutations were isolated and characterized. Five of these mutations were the result of an IS10 insertion, each generating a truncated polypeptide. The other five mutations were the same specific deletion of one amino acid, δla46. The various hns mutations exhibited different phenotypes and influenced ONA topology to variable extents. Implications for the mechanism by which H-NS influences gene expression are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-2958.1992.tb01408.x
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  • 8
    Electronic Resource
    Electronic Resource
    A protein complex mediating mRNA degradation in Escherichia coli (1994)
    Oxford, UK : Blackwell Publishing Ltd
    Molecular microbiology 14 (1994), S. 0 
    Details
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: mRNA degradation in Escherichia coli is mediated by a combination of exo- and endoribolucleases. We present evidence for a multiprotein complex which includes at least two enzymes that play important roles in mRNA degradation: the exoribonuclease poly-nucleotide phosphorylase (PNPase) and the endorlbo-nuclease RNase E. An activity which impedes the processive activity of PNPase at stem-loop structures also appears to be associated with the complex. This complex is estimated to have a molecular mass of about 500 kDa and includes several additional poly-peptides whose functions are unknown. The identification of a complex which includes several activities associated with mRNA degradation has implications for the mechanisms and co-ordinated control of mRNA degradation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-2958.1994.tb01309.x
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  • 9
    Electronic Resource
    Electronic Resource
    mRNA degradation in Escherichia coli: a novel factor which impedes the exoribonucleolytic activity of PNPase at stem-loop structures (1994)
    Oxford, UK : Blackwell Publishing Ltd
    Molecular microbiology 14 (1994), S. 0 
    Details
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: Stem-loop structures can protect upstream mRNA from degradation by impeding the processive activities of 3′–5′ exoribonucleases. The ability of such structures to impede exonuclease activity in vitro is insufficient to account for the stability they can confer on mRNA in vivo. In this study we identify a factor from Escherichia coli which specifically impedes the processive activity of the 3′–5′ exonuclease PNPase at stem-loop structures in vitro. This factor can, potentialiy, reconcile the apparent discrepancy between the ability of 3′ stem-loop structures to stabilize upstream mRNA in vitro and in vivo. Its mechanism of action, and possible role in regulating mRNA degradation, is discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-2958.1994.tb01310.x
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  • 10
    Electronic Resource
    Electronic Resource
    Role of hns in the virulence phenotype of pathogenic salmonellae (1994)
    Oxford, UK : Blackwell Publishing Ltd
    Molecular microbiology 13 (1994), S. 0 
    Details
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: A TnphoA-generated mutant C5060, attenuated for virulence, was derived from the mouse-virulent Salmonella typhimurium strain C5. This mutation, designated hns-112::TnphoA, harbours the transposon in the 3 end of hns, with the alkaline phosphatase open reading frame in the opposite orientation to that of hns. Bacterial strains harbouring hns-112::TnphoA were mucoid and had altered levels of DNA supercoiling, as monitored using pUC18 as a reporter plasmid. Transduction of hns-112::TnphoA into mouse virulent strains, including S. typhimurium SL1344 and Salmonella enteritidis Se795, resulted in attenuation. When an independent hns mutation, harbouring a kanamycin-resistance cassette inserted into the Kpnl site at base pair 237 of the hns gene, was introduced into S. typhimurium C5, the isolates were also attenuated. S. typhimurium C5 isolates harbouring the multicopy plasmid pGB651, which encodes the Escherichia coli hns gene, were partially attenuated in mice. Transductional analysis, using Tn10 insertions located close to the hns gene, showed that virulence could be restored In genetic crosses that eliminated the resident hns mutations. However, some hns+ transductants were stilt attenuated, suggesting that secondary attenuating lesions can accumulate in hns-deficient strains. These studies show that the hns locus plays a role in Salmonella virulence.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-2958.1994.tb00408.x
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