Mutation induction by 5-fluorodeoxyuridine in synchronous Chinese hamster cells.

Chinese hamster ovary cells synchronized by mitotic detachment were treated with 5-fluorodeoxyuridine (FdUrd), 0.2 micrograms/ml, at various times in the cell cycle. FdUrd treatment in the early S period induced resistance to 6-thioguanine. Treatment of asynchronous cells with FdUrd caused little increase in 6-thioguanine resistance over the spontaneous frequency. Mitotic selection thus enhances the probability of a cell being in the portion of S period receptive to mutation. These observations suggest that FdUrd treatment leads to mutagenesis at the growing points of DNA replication.