[Folding of deoxyribonucleic acid in chromatin]

A structural model for the folding of deoxyribonucleic acid (DNA) in chromatin has been evolved on the basis of the X-ray diffraction patterns of deoxyribonucleoproteids (DNP). The DNA is oriented in the direction of DNP fibres and does not exhibit a superhelical structure. In the nu-bodies the DNA is folded 7 times to and fro on the envelope of a cylinder 10 nm in diameter. The height of the DNA-hairpins is 9 nm - 10 nm. The spacing between the refolded DNA segments is 3,6 nm. This supramolecular folding crystalization of the DNA is a general principle of organization and, through different types of morphological growth of the folding crystals, leads to the chromatin, to psi-DNA, to DNA monocrystals, and to DNA packing in some phage heads.