Configurational changes in rat liver nuclear chromatin caused by azo dyes.

The effects of azo dyes on the chromatin configuration of isolated rat-liver nuclei were examined by electron microscopy for elucidation of the mechanism of dye-stimulated in vitro RNA synthesis. Sunset Yellow FCF had no effect on the incorporation of [3H]UTP into RNA but amaranth and Ponceau 3R stimulated incorporation approximately two- and 3.5-fold, respectively. Sunset Yellow FCF did not produce any major alteration in liver nuclei. Isolated liver nuclei treated with amaranth or Ponceau 3R showed dissociation of heterochromatin and the nucleoli lost their fine-granular structure acquiring a coarse-granular configuration. The dense structure of heterochromatin in liver nuclei treated with Ponceau 3R was completely dissociated and appeared as a lace-like configuration. These results suggest that both Ponceau 3R and amaranth stimulate in vitro RNA synthesis by causing the dissociation of heterochromatin in isolated rat-liver nuclei.