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 invol ved in the proteolysis of the heat-shock regulator sigma(32) and of th e phage regulator lambda cll. The hflB1(Ts) allele (formerly called ft sH1) conferring temperature-sensitive growth at 42 degrees C is suppre ssed by loss of the ferric-uptake repressor Fur and by anaerobic growt h. We show here that suppression requires TonB-dependent Fe(lll) trans port in the hflB1(Ts) fur mutant during aerobic growth at 42 degrees C and Fee-dependent Fe(ll) transport during anaerobic growth at 42 degr ees C. Temperature-resistant growth of hflB1(Ts) strains is also obser ved at 42 degrees C in the presence of a high concentration of Fe(ll), Ni(ll), Mn(ll) or Co(ll) salts, but not in the presence of Zn(ll), Cd (ll), Cu(ll), Mg(ll), Ca(ll) or Cr(lll) salts. However, neither Ni(ll) nor a fur mutation permits growth in the complete absence of HflB. Th e heat-shock response, evaluated by an hfpG::lacZ fusion, is overinduc ed in hflB1(Ts) strains at 42 degrees C because of stabilization of si gma(32). Growth in the presence of Ni(ll) or in the absence of the Fur repressor abolishes this overinduction in the hflB1(Ts) strain, and, in the hflB1(Ts) fur mutant, 32 is no longer stabilized at 42 degrees C. These results reinforce the recent observation that HflB is a metal loprotease active against sigma(32) in vitro and suggest that it can a ssociate functionally in vivo with Fe(ll), Ni(ll), Mn(ll) and Co(ll) i ons.