Figure 8. IscA is a primary target of copper toxicity.

Recombinant endonuclease III was expressed in the E. coli cells grown in LB media supplemented with or without CuSO₄. Protein was purified from the E. coli cells and subjected to UV-visible absorption measurements. A), effect of copper on the [4Fe-4S] cluster assembly in endonuclease III in the wild type and the iscA mutant cells. The E. coli cells were grown at 37°C in LB media with aeration for 3 hours. As indicated, CuSO₄ (2 mM) was added 10 min before expression of recombinant endonuclease III was induced. B), effect of copper on the [4Fe-4S] cluster assembly in endonuclease III in the E. coli copA/cueO/cusA mutant and the copA/cueO/cusA/iscA mutant cells. The E. coli cells were grown at 37°C in LB media with aeration for 3 hours. As indicated, CuSO₄ (200 μM) was added 10 min before expression of recombinant endonuclease III was induced. The protein concentration was calibrated to ~ 40 μM for the UV-visible absorption measurements.