Double Strand Breaks Induced by Low Doses of γ Rays or Heavy Ions: Quantitation in Nonradioactive Human DNA
✍ Scribed by Betsy M. Sutherland; Paula V. Bennett; John C. Sutherland
- Publisher
- Elsevier Science
- Year
- 1996
- Tongue
- English
- Weight
- 231 KB
- Volume
- 239
- Category
- Article
- ISSN
- 0003-2697
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✦ Synopsis
may sediment anomalously in neutral gradients (12, We have developed a method of quantitating low fre-24, 25); furthermore, the rate at which large molecules quencies (0-30 sites/10 9 base pairs) of double strand elute from filters at neutral pH can be affected by exbreaks in Ç1 mg of nonradioactive human DNA. Unirtrinsic factors (5, 6,13,18,22, 33,50). radiated or irradiated DNA is digested with the re-Contopoulou et al. first used pulsed-field gel electrostriction endonuclease NotI, producing cleavage fragphoresis to observe generation of double strand breaks ments that include a major group centered at Ç1.2-1.3 in Saccharomyces cerevisiae cells by ionizing radiation Mbp. The DNA molecules are separated as a function (11). Taking advantage of the fact that very large mamof size by transverse alternating field electrophoresis. malian DNAs do not enter standard neutral electropho-The frequency of double strand breaks is computed retic gels even under pulsed-field conditions, empirical directly from the decrease in number average molecumethods have been developed for measuring strand lar length induced in the 1.2-to 1.3-Mbp cleavage fragbreaks (2,4,19, 23,28,(35)(36)(37)(39)(40)(41). Radiation-inment group by 137 Cs g or Fe 26/ (1.1 GeV/nucleon) irradiduced strand breaks reduce the molecular length suffiation vs the corresponding unirradiated DNA samples. ciently such that a portion of the DNA enters the gel.
The double strand break frequency can be quantitated
The increase in the fraction of DNA entering the gel easily in the dose range of 0-10 cGy of g rays. The is then used as a measure of strand break formation. frequency of breaks per unit dose calculated for g irra-However, the fraction of DNA remaining in the well, diation of DNA in human cells (Ç4.6 double strand as estimated from the fluorescence of bound ethidium, breaks/10 9 bp/Gy) is within the range of values obdoes not agree with that determined from radiolabeling tained by others (2-8 sites/10 9 bp/Gy) who used meth-(52). Since differences in the environment of DNA in ods requiring higher doses.