DNA base and strand damage in X-irradiated monkey CV-1 cells: influence of pretreatment using small doses of radiation

Base damage in αDNA from irradiated monkey CV-1 cells was determined by measuring release of 5'-32P-end labelled DNA fragments after digestion with endonuclease III of E coli. Frequency and base sequence locations of enzyme-sensitive sites were determined. Fragments were released from irradiated DNA at sequence sites of pyrimidines and guanines. The time for repair of half the single strand breaks was approximately 1.5 h. Repair of base damage judged from loss of enzyme-sensitive sites in DNA was slower, with more than half of the damaged bases still detectable after 4h of repair. Two important changes in the pattern of fragment release from DNA were produced when small radiation doses preceded the large ones needed to produce measurable DNA strand breaks and base damage. 5 Gy to cells incubated several hours before 320 Gy increased by five-fold the abundance of small DNA fragments with 3'-phosphoryl termini detected in high-resolution denaturing gels. (author)