ADENINE-INDUCED ARREST OF MAMMALIAN-CELLS IN EARLY S-PHASE IS RELATEDTO THE PREVENTION OF DNA-SYNTHESIS INHIBITION CAUSED BY GAMMA-IRRADIATION

Adenine prevents the down-regulation of DNA synthesis in gamma-irradia ted EAT and HL60 cells. This protective effect is related to the initi ation of DNA replication. The effectiveness of this protection increas es with the concentration of adenine in both cell lines. The maximum p rotective effect of adenine induced in EAT cells occurs at about 10 ti mes lower concentration as compared with HL60 cells; however, the leve l of this effect is almost the same in both cell lines. The results in dicate that the prevention of the down-regulation of DNA synthesis in gamma-irradiated EAT and HL60 cells is conditioned mainly by the arres t of the cells in the early S-phase. It is evident that DNA synthesis in cells beyond G(1)/S boundary is insensitive to gamma-radiation.