Non-nucleosomal configuration of chromatin in nucleolar organizer regions of metaphase chromosomes in situ.

The structure of metaphase chromatin in a human tumor cell line, TG cells, was investigated using thin sections selectively stained for DNA with the Feulgen-like osmium-ammine reaction. The bulk of metaphase chromatin was characterized by the nucleosomal configuration. Some specimens were pretreated by silver staining for selective visualization of acidic proteins of the nucleolar organizer regions. In these specimens, the osmium-amine DNA tracer revealed that the chromatin present at the sites of silver granule localization had a completely extended configuration, and never gave rise to nucleosomal structures.