FIG. 9.

The accumulation of hydrogen peroxide in the cytosol contributes to the growth arrest of the Δcoa4 mutant. (A) The cytosolic catalase Ctt1 was expressed from a multi copy plasmid in the strains indicated. Note that overexpression of Ctt1 suppresses the defect observed in Δcoa4 but not in Δcmc1 cells. (B) Overexpression of Ctt1 in the intermembrane space (IMS) of mitochondria partially suppressed the growth defects of Δcmc1 and Δcoa4 mutants. (C) Model illustrating the growth arrest observed in Δcmc1 and Δcoa4 mutants. We propose that the increased production of hydrogen peroxide prevents growth of these strains under respiratory conditions. Hydrogen peroxide might be sensed outside the mitochondria, for example, to influence gene expression in the nucleus or Yca1-induced apoptosis in the cytoplasm.