The occurrence of RNA degradation triggered by H 2 O 2 was monitored during a time course between 5 and 60 min and over a broad range of concentrations (0.12-180mM for 200 min) ( Figure 1E , lanes 6-9 and Figure 2A ). Degradation was initiated relatively fast, since it was apparent at 5 min for 0.6 mM H 2 O 2 ( Figure 1E , lanes 6-9), 15-30 min for 175 mM acetic acid ( Figure 1E , lanes 1-5), 2 h for 60% glucose and 30% sorbitol ( Figure 1F ) and 3 days for ageing ( Figure 1G ) following the treatment. This onset of rRNA degradation distinctly precedes the timing of DNA damage characterized in apoptotic yeast exposed to the same stimuli (30) , indicating that RNA decay process is activated early during the response. Also, in the case of H 2 O 2 , low doses of the oxidant, starting with 0.12 mM and optimal at 0.4-3 mM, were sufficient to initiate rRNA degradation with the appearance of specific bands. When high concentration of H 2 O 2 (180 mM), believed to result in cell necrosis, was used, these specific degradation products were absent; however, the level of mature 25S and 18S rRNAs was also significantly reduced ( Figure 2A ; data not shown).