Higher-order structure of human mitotic chromosomes.

Abstract

From observations on the partial disintegration of isolated human metaphase chromosomes human metaphase chromatids are proposed to have a rather simple organization based on the folding and coiling of a long, regular, hollow cylindrical structure with a diameter of about 4000 .ANG.. This cylindrical structure, the unit fiber, is postulated to be a super-solenoid formed by the coiling of a 300 .ANG. solenoid, itself composed by coiling the basic string of nucleosomes. The structure of a human chromatid would thus be a hierarchy of helices, the contraction ratio of each coil, in ascending order of size, being approximately 7, 6, 40 and 5. This model appears to explain the estimated mass/unit length and accounts for many of the known features of human mitotic chromatids.