The Sequence Preference of Gamma-Radiation-Induced Damage in End-Labeled DNA after Heat Treatment.

In this work, we examined the DNA sequence preference of gamma-radiation-induced DNA damage in purified DNA sequences after heat treatment. DNA was fluorescently end-labeled and gamma-radiation-induced DNA cleavage was examined using capillary electrophoresis with laser-induced fluorescence detection. Our findings provide evidence that gamma-radiation-induced DNA damage to end-labeled DNA is nonrandom and has a sequence preference. The degree of cleavage was quantified at each nucleotide, and we observed that preferential cleavage occurred at C nucleotides with lesser cleavage at G nucleotides, while being very low at T nucleotides. The differences in percentage cleavage at individual nucleotides ranged up to sixfold. The DNA sequences surrounding the most intense radiation-induced DNA cleavage sites were examined and a consensus sequence 5'-AGGCC (where C is the cleavage site) was found. The highest intensity gamma-radiation-induced DNA cleavage sites were found at the dinucleotides, 5'-GG*, 5'-GC*, 5'-CC and 5'-GG and at the trinucleotides, 5'-GGC, 5'-TCA, 5'-GGG and 5'-GCC. These findings have implications for our understanding of ionizing radiation-induced DNA damage.