Abstract
This study is intended to elucidate the molecular mechanism of the mutagenesis caused by ion beam. The mutation sites caused by ion beams were determined and the mutation spectrum were compared with those induced by gamma ray.
S. cerevisiae strains used in this study are S288C(RAD+), X36B-3C(rad3), JG-18(rad18), and G160/2b(rad52).
The yeast strains were irradiated with carbon ions (12C5+; 220 MeV) with the dose 10 to 300 Gy, and LET is 107 keV/µm. Carbon ion beam was generated from AVF cyclotron in JAERI. The mutation sites of ura3 mutants were determined by DNA sequencing.
The results show that the optimum dose for mutagenesis by carbon ion beams is 100 Gy. The ion beams at 100 Gy generate mutations 168.5 fold more than spontaneous mutation.
A portion of the URA3 regions (804bp) was sequenced. Mutations generated by ion beams are dominantly transversion, whereas, mutations of spontaneous generation are usually transition. The transversion / transition ratio in the WILD type was 5.0.
Moreover, the fact that GC → TA transversion were largely observed suggests that the mutations by ion beams resulted from oxidative damage such as formation of 8-oxodGTP mainly.
Further, the mutation sites are localized on several regions with 170bp to 186bp interval. This interval may correspond to nucleosome structure.
