Ctt1 activity is upregulated by H2O2 challenge in nutrient-rich YPD and ctt1 cells exhibit lower survival than wild-type or cta1 cells. However, the three strains are equally hypersensitive to H2O2 when challenged in KPi since catalase activity falls below basal levels. Furthermore, wild-type and cta1 cells adapt to pre-challenge with a sublethal H2O2 dose in YPD but not in KPi. Thus, we conclude that Ctt1 is stimulated by H2O2 and this activity is essential in protecting yeast cells against H2O2 challenge.