Chromosome core structure revealed by silver staining.

Chromosomes were subjected to either prolonged hypotonic solution pretreatment or aging. Both conditions greatly loosened and dispersed the overlying epichromatin from the central chromosome core structure. This was followed by silver staining and examination with bright-field microscopy. The chromosome core selectively reduced the silver and stained black while the surrounding epichromatin stained yellow. A single core was seen extending the length of each chromatid. Nucleolus organizer regions appeared to be attached to the core, while kinetochores seemed to be specialized regions of the core itself. Cytochemical tests indicated that the core component(s) responsible for silver staining was non-histone protein(s).