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DFF40/CAD HYPERSENSITIVE SITES ARE POTENTIALLY INVOLVED IN HIGH MOLECULAR WEIGHT DNA FRAGMENTATION DURING APOPTOSIS

Sequential cleavage of genomic DNA into large-scale DNA fragments of 50-300-kb, followed by formation of mono- and oligonucleosomal DNA fragments, is a biochemical hallmark of programmed cell death (apoptosis). The endonuclease DFF40/CAD mediates regulated inter- nucleosomal DNA fragmentation and chromatin condensation in cells undergoing apoptosis. DFF40 hypersensitive sites were detected in purified HeLa cell nuclei, and excision of 50-kb DNA fragments preceded formation of oligonucleosomal DNA ladders in nuclei treated with the nuclease. Topoisomerase II, but not topoisomerase I, stimulates DFF40 activity on plasmid DNA substrates. This suggests that interactions of DFF with the nuclear matrix-bound topoisomerase II may be involved in formation of DFF40 hypersensitive sites.