Regulation of the heat-shock response depends on divalent metal ions in an hflB mutant of Escherichia coli.
HflB, also called FtsH, is an essential Escherichia coli protein involved in the proteolysis of the heat-shock regulator sigma 32 and of the phage regulator lambda cll. The hflB1(Ts) allele (formerly called ftsH1) conferring temperature-sensitive growth at 42 degrees C is suppressed by loss of the ferric-uptake repressor Fur and by anaerobic growth. We show here that suppression requires TonB-dependent Fe(III) transport in the hflB1(Ts) fur mutant during aerobic growth at 42 degrees C and Feo-dependent Fe(II) transport during anaerobic growth at 42 degrees C. Temperature-resistant growth of hflB1(Ts) strains is also observed at 42 degrees C in the presence of a high concentration of Fe(II), Ni(II), Mn(II) or Co(II) salts, but not in the presence of Zn(II), Cd(II), Cu(II), Mg(II), Ca(II) or Cr(III) salts. However, neither Ni(II) nor a fur mutation permits growth in the complete absence of HflB. The heat-shock response, evaluated by an htpG::lacZ fusion, is overinduced in hflB1(Ts) strains at 42 degrees C because of stabilization of sigma 32. Growth in the presence of Ni(II) or in the absence of the Fur repressor abolishes this overinduction in the hflB1(Ts) strain, and, in the hflB1(Ts) fur mutant, sigma 32 is no longer stabilized at 42 degrees C. These results reinforce the recent observation that HflB is a metalloprotease active against sigma 32 in vitro and suggest that it can associate functionally in vivo with Fe(II), Ni(II), Mn(II) and Co(II) ions.
Herman
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Institut Jacques Monod, Université Paris, France.
Lecat
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D'Ari
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Bouloc
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D049069:ATP-Dependent Proteases; D001426:Bacterial Proteins / Q000235:genetics*; D002413:Cations, Divalent; D004926:Escherichia coli / Q000235:genetics*; D029968:Escherichia coli Proteins; D005798:Genes, Bacterial; D018869:Heat-Shock Response / Q000235:genetics*; D007501:Iron / Q000494:pharmacology; D008565:Membrane Proteins / Q000235:genetics*; D026901:Membrane Transport Proteins / Q000235:genetics; D009154:Mutation; D012097:Repressor Proteins / Q000235:genetics; D013489:Suppression, Genetic
D001426:Bacterial Proteins; D002413:Cations, Divalent; D029968:Escherichia coli Proteins; D008565:Membrane Proteins; D026901:Membrane Transport Proteins; D012097:Repressor Proteins; C100775:feo protein, E coli; C068477:ferric uptake regulating proteins, bacterial; C057616:tonB protein, Bacteria; C489181:tonB protein, E coli; D007501:Iron; D049069:ATP-Dependent Proteases; C513383:FtsH protein, E coli