Double strand breaks induced by low doses of gamma rays or heavy ions: quantitation in nonradioactive human DNA.
We have developed a method of quantitating low frequencies (0-30 sites/10(9) base pairs) of double strand breaks in approximately 1 microgram of nonradioactive human DNA. Unirradiated or irradiated DNA is digested with the restriction endonuclease NotI, producing cleavage fragments that include a major group centered at approximately 1.2-1.3 Mbp. The DNA molecules are separated as a function of size by transverse alternating field electrophoresis. The frequency of double strand breaks is computed directly from the decrease in number average molecular length induced in the 1.2- to 1. 3-Mbp cleavage fragment group by 137Cs gamma or Fe26+ (1.1 GeV/nucleon) irradiation vs the corresponding unirradiated DNA samples. The double strand break frequency can be quantitated easily in the dose range of 0-10 cGy of gamma rays. The frequency of breaks per unit dose calculated for gamma irradiation of DNA in human cells (approximately 4.6 double strand breaks/10(9) bp/Gy) is within the range of values obtained by others (2-8 sites/10(9) bp/Gy) who used methods requiring higher doses.
Sutherland
B M
BM
Biology Department, Brookhaven National Laboratory, Upton, New York, 11973, USA.
Bennett
P V
PV
Sutherland
J C
JC
D002461:Cell Line, Transformed; D002588:Cesium Radioisotopes; D004247:DNA / Q000737:chemistry / Q000528:radiation effects*; D004249:DNA Damage; D015252:Deoxyribonucleases, Type II Site-Specific / Q000378:metabolism; D004586:Electrophoresis / Q000379:methods; D016521:Electrophoresis, Gel, Pulsed-Field; D006801:Humans; D007501:Iron
D002588:Cesium Radioisotopes; D004247:DNA; D007501:Iron; D015252:Deoxyribonucleases, Type II Site-Specific; C038565:GCGGCCGC-specific type II deoxyribonucleases