Different patterns of rDNA chromatin organization at NOR-1 sites.

A number of cells with a particular rDNA chromatin topology at the NOR-1 sites was observed. A - one NOR-1 site shows a terminal rDNA knob and a proximal dispersed rDNA fraction, corresponding to decondensed rDNA chromatin, while another NOR-1 site contains a rDNA knob at the proximal and the distal (satellite) end with dispersed rDNA chromatin spreading between the two; B - one NOR-1 site shows proximal rDNA knob and a terminal dispersed rDNA fraction, the other site shows only condensed rDNA chromatin at the satellite, while rDNA chromatin from the proximal part of the site is dispersed; F - fusion of the sites, i.e. very close positioning of proximal rDNA knobs in relation of each other, T - total number of analyzed cells.