[DNA packing in the DNP fibrils of polytene chromosomes]

Isolated polytene chromosomes stained with acridine orange were stretched with micromanipulator needles. Changes of chromosome fluorescence polarization led to the conclusions: 1) almost complete orientation of DNP fibers is attained at very low levels of chromosome stretching (3--8 times) without irreversible disruption of chromomeres; 2) internucleosomal DNA in native DNP fibers is supercoiled and makes 30 degrees angle to the fiber axis.