Silver staining the chromosome scaffold.

Cytological silver-staining procedures reveal the presence of a "core" running along the chromatid axes of isolated HeLa mitotic chromosomes. In this communication we examine the relationship between this "core" and the nonhistone chromosome scaffolding, isolated and characterized in previous publications from this laboratory. When chromosomes on coverslips were subjected to the steps used for scaffold isolation in vitro and subsequently stained with silver, the characteristic "core" staining was unaffected. Control experiments suggested that the "core" does not contain large amounts of DNA. When scaffolds were isolated in vitro, centrifuged onto electron microscope grids, and stained with silver, they were found to stain selectively under conditions where specific "core" staining was observed in intact chromosomes. These results suggest that the nonhistone scaffolding is the principal target of the silver stain in chromosomes.