Chromatin loop size in human leukemia (HL-60) cells

Human leukemia (HL-60) cells were treated with 0.1% detergent Joy and chromatin, protruded from the cell, was observed with an electron microscope. It was demonstrated that most, but not all of the protruded chromatin fibers had a loop structure. The average length of the protrusions of chromatin from the nucleus was 8.47 microns. A high magnification revealed that most of the protruded chromatin consisted of beaded nucleosomal fibers. Therefore, the chromatin loop size was estimated to be 315 +/- 47 k base pairs in length. This length is much longer than that of the fragmented DNA seen in the apoptosis of HL-60 cell, conflicting with the hypothesis that the DNA fragmentation is related to the size of the chromatin loop.