Enhancement of in vitro ribonucleic acid synthesis on chromium(III)-bound chromatin

Z chromatin-chromium (Cr) complex, prepared from mouse liver chromatin and CrCl3, showed a significantly enhanced template activity for in vitro RNA synthesis. Digestion experiments with this complex using micrococcal nuclease and DNase I suggested that Cr(III) preferentially binds to linker regions rather than core regions of chromatin. Further, it was found that Cr(III) binds to DNA and nonhistone proteins (NHP), but hardly to histones. Moreover, the template activity of an NHP-Cr complex, when added to a DNA-histones complex, was inhibited remarkably. The template activity of the chromatin-Cr complex was not significantly altered by proteinase K digestion. Furthermore, experiments using rifampicin and [gamma-32P]guanosine 5'-triphosphate (GTP) demonstrated an increase in the number of initiation sites in the chromatin-Cr complex. These results suggest that, in this in vitro system, Cr(III) preferentially binds to DNA in chromatin and causes an increase in the number of initiation sites, thus enhancing RNA synthesis.