Fig. 6. Mapping of MAR elements in AML-BCR3 and ETO-BCR2. Different fragments present in the input mixture are shown by arrows at the left-hand side of the lane with input DNA. The other four lanes in each experiment represent the fragments obtained from the nuclear matrix incubated with the input fragments in the presence of increasing amounts (50 µg ml^–1, 100 µg ml^–1, 200 µg ml^–1 and 500 µg ml^–1) of cold, non-specific competitor DNA (sheared Escherichia coli DNA), whereas the amount of labeled input DNA was constant (1 µg ml^–1) in all cases. Notice that the 900 bp subfragment of ETO-BCR2 and the 1200 bp subfragment of AML-BCR3 are retained by nuclear matrices to the same extent as bona fide MARs from the Drosophila histone gene cluster (`Hist-MAR'), whereas the other subfragments of the BCRs and the pUC DNA are washed out at high concentrations of non-specific competitor DNA.