FIG 9.

Clp proteins sustain the intracellular pools of free iron during H₂O₂ stress. (A) The ClpX protein increases the vulnerability of cells to oxidative DNA damage. Cells were aerated for 2 h and then exposed to cysteine and 2.5 mM H₂O₂. After 2 min of H₂O₂, cell survival was determined by colony formation. The combination of cysteine and millimolar H₂O₂ triggers the production of hydroxyl radicals by cellular pools of loose iron. The dashed line represents 100% survival. (B) The Clp proteins increase the intracellular pool of free iron that can be detected by EPR. Hpx⁻ cells were aerated for 2 h before measurements. (C) The expression of the Fur:Fe(II)-repressed iucC-lacZ fusion was determined after 2 h of aeration. Elevated expression indicates that the intracellular loose-iron pools are inadequate for full protein metallation. Strains: LC106, ASE7, ASE11, ASE21, ASE67, ASE119, ASE125, MS100, ASE412, MS103, and ASE425.