THE EFFECT OF ~(60)CO-IRRADIATION ON SYNTHESIS OF DNA AND HISTONE IN CHINESE HAMSTER OVARY FIBRILBLAST CELLS
ZHAO JI-YING,LEE JING-FU,WANG QLNG-ZI AND ZHANG XIU-ZNEN (Institute of Biophysics,Academia Sinica)
The relationship between histonesynthesis and DNA synthesis in asynchronized and S phase synchronizedCHO cells following γ-irradiation wasinvestigated.Radiation dose was 4——60Gy with dose rate of 0.78 Gy/min.The DNA and histone content ofboth irradiated and unirradiated cellsdoubly labelled with ~3H-thymidine and~(14)C-alanine were determined and thepolyacrylamide gel electrophoresis method was used to display the radiationinduced changes in histone composi-tion.The results have shown: 1) The DNA and histone syn-thesis were inhibited to some extent inboth asynchronized and S phase syn-chronized cells following irradiation,degree of inhibition being increasedwith irradiation dose. 2) The incorporation of ~3H-thy-midine and ~(14)C-alanine into CHOcells was significantly inhibited in thefirst 3 hours after irradiation of 16Gy,from the 4th hour the incorporationrate of ~(14)G-alanine began to recoverand almost backed to normal at the48th hour after irradiation,but theincorporation of ~3H-thymidine wasstill depressed during this period. 3) The rate of DNA synthesis inasynchronous cells was more seriouslydepressed than that in synchronouscells of G_1 stage at the 8th hour afterirradiation. 4) The histone was extractedfrom both irradiated and controlledcells by 0.25 N HCL,and then frac-tionted by polyacrylamide gel elec-trophoresis.It was shown that after irradiation H_1 and H_3 histonebands were markedly deminished.Itis supposed that there may exists certain coupling between DNA synthesis and the synthesis of H_1 and H_2histone.