it is possible either that ( 1 ) topoisomerase ii is altered in strain ly-s and that this enzyme is involved in the repair of dna double-strand breaks or ( 2 ) strain ly-s is deficient in a reaction which is necessary for the repair of dna double-strand breaks induced by ionizing radiation as well as the repair of dna damage induced by these topoisomerase ii inhibitors . m-amsa , vp-16 , and ellipticine were found to be highly mutagenic at the tk locus in l5178y strains which are heterozygous for the tk gene but not in a tk hemizygous strain , indicating that these inhibitors induce multilocus lesions in dna , as does ionizing radiation .
C1511667
dna double-strand breaks
C0012899
repair