The Synthesis of Deoxyribonucleic Acid and Nuclear Proteins by Rat Hepatoma Cells Immediately after Gamma Irradiation

Rat hepatoma cells were irradiated with 1000 rads of gamma radiation in vivo 7 days after intraperitoneal inoculation. Cells were removed immediately after exposure and incubated in medium containing radioactive amino acids or radioactive thymidine. Incorporation of these precursors was monitored for the first half hour, during which DNA and nuclear proteins were normally synthesized at a constant rate. The incorporation of radioactive thymidine into DNA after 1000 rads was about half that found in unirradiated cells, and the incorporation of amino acids into histones and urea-soluble nuclear proteins was unaffected during the first half hour. The presumed normal relationship between DNA synthesis and nuclear protein synthesis appears not to be maintained in irradiated ascites tumor cells.