Recovery from transcription inhibition in irradiated yeast cells.

Repair process operating on radiation damaged DNA may be investigated by studying its functional integrity, e.g. its ability to serve as template for transcription. We measured the synthesis of ribosomal RNA and of the inducible enzyme arginase in yeast cells and followed their recovery after X-ray, alpha-particle and heavy ion exposure. Transcription inhibiting lesions formed upon X-irradiation in yeast cells are repaired during post-exposure incubation ("liquid-holding"). The inactivation curves are strictly exponential immediately after irradiation. After the "liquid holding" treatment the inactivation curves are still exponential but with a progressive decrease of the slopes as a function of incubation time. This indicates that a constant fraction of the lesions is repaired per time interval. But even after long incubation times (24 h) there is still a sizeable unrepaired fraction. Comparing different yeast strains and different irradiation temperatures recovery can also be demonstrated in cells exposed to alpha-particles. In addition, recovery is detected by the arginase assay after irradiation of yeast with very heavy charged particles, e.g. titanium ions.