YIELD OF DNA-PROTEIN CROSS-LINKS IN GAMMA-IRRADIATED CHINESE-HAMSTER CELLS

  • 15 April 1987
    • journal article
    • research article
    • Vol. 47  (8) , 2032-2035
Abstract
.gamma.-Irradiation of Chinese hamster V79 cells increases the percentage of nuclear DNA cross-linked to proteins. Studies were carried out to ascertain whether the radiation-induced increase in DNA-protein crosslinks (DPC) is due to an increase in the number of DNA fragments which are cross-linked to protein or to an increase in the size of bound DNA fragments. Cells were prelabeled with [3H]thymidine and irradiated (10-600 Gy), and DPCs were collected on nitrocellulose filters. Native gel analysis of the DNA recovered from the filters indicate that the number average molecular weight of cross-linked DNA (1.22 .times. 107 Da) is the same in unirradiated cells and in cells given up to 100 Gy. Assuming 5 pg of DNA per V79 cell, it was possible to calculate that there are approximately 6 .times. 103 DPC per unirradiated cell and that 150 DPC are formed per gray of .gamma.-radiation for doses of 0-100 Gy. Thus, radiation increases the number of new linkages between DNA and protein. At radiation doses greater than 200 Gy the percentage of nuclear DNA cross-linked to protein approaches a plateau value. The number of DPC (>6 .times. 104) formed at higher doses is within the range of the estimated number of DNA attachment sites on the nuclear matrix.