Agarose gel electrophoresis (1%) of cell lines stained with ethidium-bromide. Each DNA sample is shown before heat denaturation and after heat denaturation. Nalm6 (lines 1, 2) and U937 (lines 7,8) DNA is high molecular and less fragmented than DNA from mutant ALL-1 bearing cells B1B (lines 3,4) and ML-2 (lines 5,6).
