RNA synthesis in Yoshida ascites tumor cells after ultraviolet and gamma irradiation.

The residual RNA synthesis in Yoshida ascites tumor cells following exposure to ultraviolet radiation was insensitive to rifampicin AF/013, an inhibitor of initiation of RNA synthesis in eukaryotic cells. On the other hand, residual RNA synthesis in the ascites tumor cells after gamma-irradiation was inhibited by rifampicin AF/013. In vitro synthesis of RNA on ultraviolet-irradiated ascites chromatin likewise was resistant to rifampicin AF/013. Ultraviolet irradiation was found to decrease the number of RNA chain initiation sites on ascites chromatin considerably whereas the number of initiation sites on ascites chromatin increased considerably after gamma irradiation. These results indicate that ultraviolet irradiation may preferentially affect the DNA segments participating in initiation of RNA synthesis.