Induction of chromosomal aberrations in Chinese hamster ovary cells by the restriction endonuclease Dra I: dose-effect relationships and effect of substitution of chromosomal DNA with bromodeoxyuridine

Treatment of G1-phase Chinese hamster ovary (CHO) cells with the restriction endonuclease Dra I (recognition site TTT/AAA) leads to the induction of chromosome-type aberrations. The dose-effect relationships or the frequencies of polycentric chromosomes have a strong linear component. Prelabelling of the cells with bromodeoxyuridine (B) leads to a strong suppression by the chromosome breaking activity of Dra I. This may be explained by assuming that substitution of T by B renders the recognition site of Dra I resistant to being cut by the enzyme.