The dnaKJ operon belongs to the sigma32-dependent class of heat shock genes in Bradyrhizobium japonicum.
The dnaKJ genes of Bradyrhizobium japonicum were cloned and sequenced. They map adjacent to each other, as in other proteobacteria of the alpha and gamma subgroups. Primer extension experiments identified two strongly heat-inducible transcripts starting 99 bp (T1) and 204 bp (T2) upstream of dnaK. Synthesis of the shorter transcript T1 in Escherichia coli required the presence of a recently characterized sigma32 homologue (RpoH1) from B. japonicum. The -35 and -10 regions of the promoters associated with the transcription start sites T1 and T2 displayed nucleotide sequence motifs that are characteristic for sigma32-dependent promoters in E. coli and alpha-proteobacteria. Heat shock regulation of dnaK expression was confirmed by immunoblot analysis of DnaK protein. All of these results put dnaK into the sigma32-dependent class, not the CIRCE-dependent class, of heat shock genes in B. japonicum. At normal growth temperature dnaK was expressed at a significant basal level. All attempts to eliminate dnaK function by insertion or deletion mutagenesis failed. By contrast, dnaJ null mutants and insertions in the dnaKJ intergenic region were easily obtained. The growth rate of dnaJ mutants was reduced but the final cell density reached in rich medium and their symbiotic properties were indistinguishable from the wild type.
Minder
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Mikrobiologisches Institut, Eidgenossische Technische Hochschule, Zurich, Switzerland.
Narberhaus
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Babst
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Hennecke
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Fischer
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HM
D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000235:genetics; D001483:Base Sequence; D003001:Cloning, Molecular; D004252:DNA Mutational Analysis; D017931:DNA Primers / Q000235:genetics; D004269:DNA, Bacterial / Q000235:genetics; D029968:Escherichia coli Proteins; D005798:Genes, Bacterial; D005816:Genetic Complementation Test; D050956:HSP40 Heat-Shock Proteins; D018840:HSP70 Heat-Shock Proteins / Q000096:biosynthesis / Q000235:genetics*; D006360:Heat-Shock Proteins / Q000235:genetics*; D006358:Hot Temperature; D008969:Molecular Sequence Data; D009876:Operon; D011401:Promoter Regions, Genetic; D012230:Rhizobiaceae / Q000235:genetics* / Q000378:metabolism; D012808:Sigma Factor / Q000235:genetics; D014157:Transcription Factors
D001426:Bacterial Proteins; D017931:DNA Primers; D004269:DNA, Bacterial; C494635:DnaJ protein, E coli; D029968:Escherichia coli Proteins; D050956:HSP40 Heat-Shock Proteins; D018840:HSP70 Heat-Shock Proteins; D006360:Heat-Shock Proteins; D012808:Sigma Factor; D014157:Transcription Factors; C069774:heat-shock sigma factor 32; C063842:dnaK protein, E coli