Mutation induction by charged particles of defined linear energy transfer (LET) and γ rays was scored using human-hamster hybrid A L cells. The LET values for charged particles accelerated at the Radiological Research Accelerator Facility ranged from 10 keV/μm protons to 150 keV/μm4 He ions. The induced mutant fractions at both the S1 and HGPRT loci were dependent on the dose and LET. In addition, for each dose examined, the mutant yield at the S1 locus was 30-60-fold higher than at the corresponding HGPRT locus. To determine whether the mutation spectrum was comparably dependent on dose and LET, independent <tex-math>${\rm S}1^{-}$</tex-math> and <tex-math>${\rm HGPRT}^{-}$</tex-math> mutants induced by 150 keV/μm4 He ions and γ rays were isolated, and their DNA was analyzed by both Southern blotting and multiplex PCR methods. While the majority of radiation-induced mutants showed deletions of varying sizes, the relative percentage of large deletions was found to be related to both the dose and LET of the radiation examined. Using a mutation system that can detect multilocus changes, results of the present study show that radiation-induced chromosomal loss can be in the millions of base pairs.

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