A rapid downshift in the growth temperature of Saccharomyces cerevisiae from 30 to 10 degreesC resulted in an increase in transcript levels of the antioxidation genes SOD1 [encoding Cu-Zn superoxide dismutase (SOD)], CTT1 (encoding catalase T), and GSH1 (encoding gamma-glutamylcysteine synthetase). The cellular activities of SOD and catalase were also increased, indicating that the temperature downshift caused an antioxidant response. In support of this, a simultaneous increase in the intracellular level of H2O2 was observed. The level of YAP1 mRNA, encoding a transcription factor critical for the oxidative stress response in this yeast, was also increased by the temperature downshift. However, deletion of YAP1 did not reduce the elevated mRNA levels of the antioxidant genes. This suggests that the temperature down shift-induced increase in the mRNA level of anti-oxidant genes is YAP1 independent. (C) 2003 Elsevier Inc. All rights reserved.