In addition to the 25S rRNA, other rRNA species were also probed for undergoing specific decay. After treatment with H 2 O 2 , RNA damage with accumulation of characteristic breakdown products occurred for 5.8S and, to a much lesser extent, for 18S, but not for 5S, (Figure 1B and C; data not shown). In the case of 18S, hardly any degradation intermediates were detected, there was some decay of the mature RNA, however, it was approximately 2.5 to 3-fold weaker than for the mature 25S. Therefore, we conclude that mainly the two components of the large ribosomal subunit, 25S and 5.8S, undergo specific apoptotic degradation.