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  • 1
    Electronic Resource
    Electronic Resource
    Catabolite regulation of two Escherichia coli operons encoding nitrite reductases: role of the Cra protein (1997)
    Springer
    Archives of microbiology 168 (1997), S. 240-244 
    Details
    ISSN: 1432-072X
    Keywords: Key words Catabolite regulation ; Cra protein ; Nitrite ; reductase regulation ; Escherichia coli ; Catabolite ; repression
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The Escherichia coli nir and nrf operons, which encode alternative nitrite reductases expressed during anaerobic growth, are subject to catabolite regulation. Transcription from the nir promoter is maximal when bacteria are grown in rich media such as Lennox broth supplemented with glucose. Conversely, expression of the nrf operon is suppressed by rich media, but stimulated during growth in minimal medium with glycerol and fumarate. The role of the catabolite repressor-activator (Cra) protein in catabolite regulation of the nir and nrf promoters was investigated. Transcription from the nir promoter was repressed by Cra when cells were grown in minimal medium with glycerol and fumarate. Crude protein extracts from a strain overproducing Cra encoded on a multicopy plasmid retarded a nir promoter fragment in a mobility shift assay, confirming that the observed Cra-dependent repression was due to the direct interaction of Cra with the regulatory region of the nir operon. Furthermore, the inclusion of fructose 1-phosphate, an effector of Cra DNA-binding activity, in the assay decreased the ability of Cra to retard the nir promoter fragment. In contrast, transcription from the nrf promoter was not regulated by Cra under any of the growth conditions tested.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002030050494
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  • 2
    Electronic Resource
    Electronic Resource
    Characterisation of Escherichia coli K-12 mutants defective in formate-dependent nitrite reduction: essential roles for hemN and the menFDBCE operon (1997)
    Springer
    Archives of microbiology 168 (1997), S. 403-411 
    Details
    ISSN: 1432-072X
    Keywords: Key words Nitrite reductase mutants ; Formate-dependent nitrite reduction ; Anaerobic electron transfer ; Menaquinones ; hemN ; Cytochrome c biosynthesis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Three Escherichia coli mutants defective in formate-dependent nitrite reduction (Nrf activity) were characterised. Two of the mutants, JCB354 and JCB356, synthesized all five c-type cytochromes previously characterised in anaerobic cultures of E. coli. The third mutant, JCB355, was defective for both cytochrome b and cytochrome c synthesis, but only during anaerobic growth. The insertion sites of the transposon in strains JCB354 and JCB356 mapped to the menFDBCE operon; the hemN gene was disrupted in strain JCB355. The mutation in strain JCB354 was complemented by a plasmid encoding only menD; strain JCB356 was complemented by a plasmid encoding only menBCE. A mutant defective in the methyltransferase activity involved in both ubiquinone synthesis and conversion of demethylmenaquinone to menaquinone expressed the same Nrf activity as the parental strain. The effects of men, ubiA and ubiE mutations on other cytochrome-c-dependent electron transfer pathways were also determined. The combined data establish that menaquinones are essential for cytochrome-c-dependent trimethylamine-N-oxide reductase (Tor) and Nrf activity, but that either menaquinone or ubiquinone, but not demethylmenaquinone, can transfer electrons to a third cytochrome-c-dependent electron transfer chain, the periplasmic nitrate reductase.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002030050515
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    Effects of mutations in genes for proteins involved in disulphide bond formation in the periplasm on the activities of anaerobically induced electron transfer chains in Escherichia coli K12 (1996)
    Springer
    Molecular genetics and genomics 253 (1996), S. 95-102 
    Details
    ISSN: 1617-4623
    Keywords: Key words Disulphide bond formation ; Cytochrome c assembly ; Nitrite reduction ; Nitrate reduction ; Escherichia coli
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract  The assembly of anaerobically induced electron transfer chains in Escherichia coli strains defective in periplasmic disulphide bond formation was investigated. Strains deficient in DsbA, DsbB or DipZ (DsbD) were unable to catalyse formate-dependent nitrite reduction (Nrf activity) or synthesize any of the known c-type cytochromes. The Nrf+ activity and cytochrome c content of mutants defective in DsbC, DsbE or DsbF were similar to those of the parental, wild-type strain. Neither DsbC expressed from a multicopy plasmid nor a second mutation in dipZ (dsbD) was able to compensate for a dsbA mutation by restoring nitrite reductase activity and cytochrome c synthesis. In contrast, only the dsbB and dipZ (dsbD) strains were defective in periplasmic nitrate reductase activity, suggesting that DsbB might fulfil an additional role in anaerobic electron transport. Mutants defective in dipZ (dsbD) were only slightly more sensitive to Cu++ ions at concentrations above 5 mM than the parental strain, but strains defective in DsbA, DsbB, DsbC, DsbE or DsbF were unaffected. These results are consistent with our earlier proposals that DsbA, DsbB and DipZ (DsbD) are part of the same pathway for ensuring that haem groups are attached to the correct pairs of cysteine residues of apocytochromes c in the E. coli periplasm. However, neither DsbE nor DsbF are essential for the reduction of DipZ (DsbD).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/PL00013815
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    Paper (German National Licenses)
    Fulltext
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