Abstract
The ion beams were widely used as the mutagen for plants and also used for cancer therapy. However, precise effect of ion beams to DNA molecules is not yet elucidate. The molecular mechanism of the mutagenesis caused by carbon ion beams was studied. The mutation sites caused by ion beams were determined and the mutation spectrums were compared with those induced by gamma ray.
S. cerevisiae strains used in this study are S288C (RAD+), rad52 and ogg1. RAD52p is a component the homologous recombination repair pathway. OGG1p is a DNA glycosylase / AP lyase that excises guanine lesions such as 8-oxoguanine (8-oxoG).
The yeast strains were irradiated with carbon ions (220 MeV) with the dose 10 to 100 Gy, and LET is 107 keV/μm. Carbon ion beams were generated from AVF cyclotron in JAEA. The mutation sites of ura3 mutants were determined by DNA sequencing.
The URA3 regions of mutants were sequenced. The carbon ion induced more transversions than transitions, deletions or insertions. Moreover, the fact that GC to TA transversions largely observed suggests that the mutations by ion beams resulted from oxidative damage such as formation of 8-oxodG mainly, and the remarkable feature of yeast mutations induced by carbon ions was that the mutations sites were localized near the linker regions of nucleosomes.
