DECREASE IN CATALASE ACTIVITY AND LOSS OF THE 11P CHROMOSOME ARM IN THE COURSE OF SV40 TRANSFORMATION OF HUMAN FIBROBLASTS

The activity of catalase, a key enzyme in cell detoxication of oxygen derivatives, was studied in SV40 transformed human fibroblasts. A cyto genetic study was performed in parallel to establish a quantification of 11p arm on which the corresponding gene is mapped. mRNA amounts wer e determined by Northern blotting. At early passages, catalase activit y strongly decreased whereas the corresponding MRNA was present. No de letions of 11p arms were detected. At later passages, catalase activit y remained low. 11p arm deletions were frequent, and the amount of mRN A was decreased. In these late passages, the good correlation between the number of 11p arms and catalase activity suggested a gene dosage e ffect. It is assumed that the decrease of catalase activity provides a selective advantage for the transformed cells. This decrease is relat ed to a post-transcriptional change of regulation at early passages an d to the loss of the corresponding gene at later passages.