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  • 11
    Electronic Resource
    Electronic Resource
    Increase in negative supercoiling of plasmid DNA in Escherichia coli exposed to cold shock (1997)
    Oxford BSL : Blackwell Science Ltd
    Molecular microbiology 23 (1997), S. 0 
    Details
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: Negative supercoiling of plasmid DNA in Escherichia coli cells can decrease transiently when exposed to heat shock. The effect of cold shock on DNA supercoiling was examined, and analysis by agarose gel electrophoresis in the presence of chloroquine revealed that negative supercoiling of plasmid DNA in cells increased when cells were exposed to cold shock. This increase was transient and was nil when the cells were pretreated with nalidixic acid, an inhibitor of DNA gyrase. In a mutant deficient in expression of HU protein, the increase in negative supercoiling of DNA by cold shock is less apparent than in wild-type cells. It is proposed that DNA gyrase and HU protein have a role in the DNA supercoiling reaction seen with cold shock.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2958.1997.2181582.x
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  • 12
    Electronic Resource
    Electronic Resource
    CedA is a novel Escherichia coli protein that activates the cell division inhibited by chromosomal DNA over-replication (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: We isolated and characterized a new gene related to the control of cell division regulation in Escherichia coli. At 30°C, the dnaAcos mutant causes over-replication of the chromosome, and colony formation is inhibited. We found that, at this temperature, the dnaAcos cells form filaments; therefore, septum formation is inhibited. This inhibition was independent of SfiA, an inhibitor of the septum-forming protein, FtsZ. To identify factors involved in this pathway of inhibition, we isolated seven multicopy suppressors for the cold-sensitive phenotype of the dnaAcos mutant. One of these proved to be a previously unknown gene, which we named cedA. This gene encoded a 12 kDa protein and resided at 38.9 min on the E. coli genome map. A multicopy supply of the cedA gene to the dnaAcos cells did not repress over-replication of the chromosome but did stimulate cell division of the host, the result being growth of cells with an abnormally elevated chromosomal copy number. Therefore, the expression level of the cedA gene seems to be important for inhibiting cell division of the dnaAcos mutant at 30°C. We propose that over-replication of the chromosome activates a pathway for inhibiting cell division and that the cedA gene modulates this division control. In the dnaA+ background, cedA also seems to affect cell division.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2958.1997.5941967.x
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  • 13
    Electronic Resource
    Electronic Resource
    Mutant DnaA proteins defective in duplex opening of oriC, the origin of chromosomal DNA replication in Escherichia coli (2000)
    Oxford BSL : Blackwell Science Ltd
    Molecular microbiology 35 (2000), S. 0 
    Details
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: We characterized three mutant DnaA proteins with an amino acid substitution of R334H, R342H and E361G that renders chromosomal replication cold (20°C) sensitive. Each mutant DnaA protein was highly purified from overproducers, and replication activities were assayed in in vitro oriC replication systems. At 30°C, all three mutant proteins exhibited specific activity similar to that seen with the wild-type protein, whereas at 20°C, there was much less activity in a replication system using a crude replicative extract. Regarding the affinity for ATP, the dissociation rate of bound ATP and binding to oriC DNA, the three mutant DnaA proteins showed a capacity indistinguishable from that of the wild-type DnaA protein. Activity for oriC DNA unwinding of the two mutant DnaA proteins, R334H and R342H, was more sensitive to low temperature than that of the wild-type DnaA protein. We propose that R334H and R342H have a defect in their potential to unwind oriC DNA at low temperatures, the result being the cold-sensitive phenotype in oriC DNA replication. The two amino acid residues of DnaA protein, located in a motif homologous to that of NtrC protein, may play a role in the formation of the open complex. The E361 residue may be related to interaction with another protein present in a crude cell extract.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2958.2000.01722.x
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  • 14
    Electronic Resource
    Electronic Resource
    Overinitiation of chromosome replication in the Escherichia coli dnaAcos mutant depends on activation of oriC function by the dam gene product (1997)
    Oxford, UK : Blackwell Science Ltd
    Molecular microbiology 25 (1997), S. 0 
    Details
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: The activity of DnaA protein, the initiator of chromosome replication in Escherichia coli, is regulated by adenine nucleotide binding; the ATP-bound form, not the ADP-bound form, is active. DnaAcos is a mutant protein that is insensitive to negative regulation by ADP. Initiation of chromosome replication occurs excessively in the dnaAcos mutant at 30°C, a restrictive temperature for growth. To determine the control factors that act independently of adenine nucleotide binding of DnaA, we analysed suppressors from the dnaAcos mutant isolated by Tn5 insertion mutagenesis. Three of the suppressors carried Tn5 in the aroK or aroB gene, the first two cistrons in the dam operon. Complementation tests revealed that the dam gene is responsible for the suppression. Over-replication of the chromosome was inhibited in the dnaAcos aroK::Tn5 double mutant, and initiation of chromosome replication in the dnaA+aroK::Tn5 mutant was partially inhibited. The aroK (or B )::Tn5 cells contained DnaA molecules at a level similar to that in the parental aroBK + strain. Moreover, dnaAcos suppression depended on the function of the seqA gene. Thus, Dam activity positively regulates initiation of chromosome replication in vivo. SeqA function seems to be distinguished from the control of DnaA protein by adenine nucleotide binding.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2958.1997.5001872.x
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  • 15
    Electronic Resource
    Electronic Resource
    Characterization of Escherichia coli DnaAcos protein in replication systems reconstituted with highly purified proteins (1995)
    Osney Mead, Oxford OX2 0EL, UK : Blackwell Science Ltd
    Molecular microbiology 18 (1995), S. 0 
    Details
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: Excessive initiation of chromosomal replication occurs in the dnaAcos mutant at 30°C. Whereas purified wild-type DnaA protein binds ATP and ADP tightly, DnaAcos protein is defective for such nucleotide binding. As initiation is a multistep reaction and DnaA protein functions at each step, activities of DnaAcos protein need to be examined precisely. DnaAcos protein specifically bound a DNA fragment containing the chromosomal replication origin with an affinity similar to that seen with the wild-type protein. In a system reconstituted with purified proteins at 30°C, the mutant protein initiated replication of single-stranded DNA that contains a DnaA-binding hairpin structure. Thus, DnaAcos protein basically sustains affinity to a DnaA-binding sequence and functions in the loading of DnaB helicase onto single-stranded DNA. Thermal stabilities of wild-type DnaA and DnaAcos activities were comparable. Unlike wild-type DnaA protein, DnaAcos protein was inactive for minichromosomal replication in systems reconstituted with purified proteins in which the ATP-bound form of DnaA protein is required for initiation. Taken together, the data indicate that the prominent defect in DnaAcos protein appears to be the inability to bind nucleotide.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-2958.1995.18050813.x
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  • 16
    Electronic Resource
    Electronic Resource
    Silkworm pathogenic bacteria infection model for identification of novel virulence genes (2005)
    Oxford, UK : Blackwell Science Ltd
    Molecular microbiology 56 (2005), S. 0 
    Details
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: Silkworms are killed by injection of pathogenic bacteria, such as Staphylococcus aureus and Streptococcus pyogenes, into the haemolymph. Gene disruption mutants of S. aureus whose open reading frames were previously uncharacterized and that are conserved among bacteria were examined for their virulence in silkworms. Of these 100 genes, three genes named cvfA, cvfB, and cvfC were required for full virulence of S. aureus in silkworms. Haemolysin production was decreased in these mutants. The cvfA and cvfC mutants also had attenuated virulence in mice. S. pyogenes cvfA-disrupted mutants produced less exotoxin and had attenuated virulence in both silkworms and mice. These results indicate that the silkworm-infection model is useful for identifying bacterial virulence genes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-2958.2005.04596.x
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  • 17
    Electronic Resource
    Electronic Resource
    Isolation and characterization of inhibitory factors of DNA polymerase III holoenzyme from Escherichia coli (1995)
    Oxford, UK : Blackwell Publishing Ltd
    FEMS microbiology letters 130 (1995), S. 0 
    Details
    ISSN: 1574-6968
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Abstract We isolated fractions by Mono Q chromatography that inhibited the activity of Escherichia coli DNA polymerase III holoenzyme using an assay system with a primed single-stranded DNA template coated with single-stranded DNA binding protein (SSB). The inhibitory activities were inactivated by heat-treatment at 100 °C for 10 min, suggesting that they are proteins. The factors did not inhibit the activity of RNA polymerase of Escherichia coli. The inhibitory effects were less potent for the activities of the large (Klenow) fragment of DNA polymerase I and T4 DNA polymerase than for DNA polymerase HI holoenzyme. No degradation of single-or double-stranded DNA was observed in the fractions, indicating that inhibition was not due to degradation of the DNA.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1574-6968.1995.tb07723.x
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  • 18
    Electronic Resource
    Electronic Resource
    Relaxation of supercoiled DNA associated with induction of heat shock proteins in Escherichia coli (1993)
    Springer
    Molecular genetics and genomics 238 (1993), S. 1-5 
    Details
    ISSN: 1617-4623
    Keywords: DNA relaxation ; DNA supercoiling ; DNA gyrase ; Heat shock response ; rpoH
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Heat treatment of wild-type Escherichia coli cells led to a transient relaxation of negatively supercoiled plasmid DNA and there was no recovery of DNA torsional strain in the DNA in gyrA mutant cells. After heat treatment, DnaK and GroEL proteins were synthesized continuously in the gyrA mutant cells, whereas they were synthesized only transiently in wild-type cells. Thus, change in superhelical density of the DNA correlated with the temperature-induced expression of heat shock proteins. Inhibitors of DNA gyrase (nalidixic acid, novobiocin), an organic solvent (ethanol) and a psychotropic drug (chlorpromazine) all stimulated relaxation of cellular DNA over the same concentration range that induces heat shock proteins. As DNA relaxation was induced by heat treatment or chemicals in an rpoH mutant, the process is not the result of induced synthesis of heat shock proteins.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00279523
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  • 19
    Electronic Resource
    Electronic Resource
    Co-induction of DNA relaxation and synthesis of DnaK and GroEL proteins inEscherichia coli by expression of LetD (CcdB) protein, an inhibitor of DNA gyrase encoded by the F factor (1996)
    Springer
    Molecular genetics and genomics 250 (1996), S. 593-600 
    Details
    ISSN: 1617-4623
    Keywords: DNA relaxation ; Heat shock response ; LetD (CcdB) protein ; DNA gyrase ; σ 32
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract We examined the influence of overexpression of LetD (CcdB) protein, an inhibitor of DNA gyrase encoded by the F factor ofEscherichia coli, on DNA supercoiling and induction of heat shock proteins. Cells were transformed with a plasmid carrying the structural gene for LetD protein under control of thetac promoter, and LetD protein was induced by adding isopropylβ-d-thiogalactopyranoside (IPTG) to the culture medium. Analysis by agarose gel electrophoresis in the presence of chloroquine revealed relaxation of plasmid DNA in cells depending on the concentration of IPTG employed for induction. Protein pulse-labeling experiments with [35S]methionine and cysteine revealed that synthesis of DnaK and GroEL proteins was also induced by IPTG, and concentrations necessary for DNA relaxation and induction of the heat shock proteins were much the same. Expression of mutant LetD protein lacking two amino acid residues at the C-terminus induced neither DNA relaxation nor the synthesis of DnaK and GroEL proteins. Induction of wild-type LetD protein but not mutant LetD protein markedly enhanced synthesis ofσ 32. We interpret these results to mean that DNA relaxation in cells caused by the expression of LetD protein induces heat shock proteins via increased synthesis ofσ 32.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02174447
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  • 20
    Electronic Resource
    Electronic Resource
    Phenotypes of dnaA mutants of Escherichia coli sensitive to phenothiazine derivatives (1996)
    Springer
    Molecular genetics and genomics 252 (1996), S. 212-215 
    Details
    ISSN: 1617-4623
    Keywords: Key wordsEscherichia coli ; Phenothiazine derivatives ; DnaA protein
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The activation of DnaA protein by cardiolipin is inhibited by fluphenazine in vitro. We therefore examined the sensitivity of temperature-sensitive dnaA mutants of Escherichia coli to fluphenazine and other phenothiazine derivatives. Among the eight dnaA mutants tested, dnaA5, dnaA46 dnaA602, and dnaA604, mutants with mutations in the putative ATP binding site of DnaA protein, showed higher sensitivities to phenothiazine derivatives than did the wild-type strain. The dnaA508 and dnaA167 mutants, which have mutations in the N-terminal region of DnaA protein, also showed higher sensitivities to phenothiazine derivatives. On the other hand, the dnaA204 and dnaA205 mutants, with lesions in the C-terminal region of the DnaA protein, showed the same sensitivity to phenothiazine derivatives as the wild-type strain. Complementation analysis with a plasmid containing the wild-type dnaA gene and phage P1-mediated transduction confirmed that dnaA mutations are responsible for these sensitivity phenotypes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004389670024
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