[Relative positions of stainable portions of DNA in deoxyribonucleoprotein fibrils].

The effect of acridine orange (AO) concentration on fluorescence polarization of DNA, DNP100 and DNP250 solutions (100 A and 249 A thick DNP fibers, respectively) was studied. It was shown that fluorescence depolarization by an excitation energy migration mechanisms is 3.5 times more efficient for DNP250 than for DNP100. Higher efficiency of energy migration may be explained by a tighter packing of stained DNA regions inside the 250 A fiber because both DNP100 and DNP250 have equal numbers of AO binding sites. The calculated average number of packed DNA strands in DNP250 is 3, the average angle between them is 26.5 degrees. A model of the 250 A DNP fiber is proposed. In this model nucleosomes form a tight 250 A coil with a 430 A pitch, internucleosomal DNA strands are oriented approximately along the fiber axis.