Deletion of stably integrated DNA is suppressed by cadmium and zinc

The bacterial xanthine-guanine phosphoribosyltransferase (GPT) gene was fused to a metal-responsive promoter and transfected into a murine cell line. Clonal transformants harboring metal-responsive or nonresponsive GPT genes (using a thymidine kinase promoter) were then studied for the loss of transfected gene function either during periods of constitutive expression or during periods of induced activity. Nontoxic levels of cadmium and zinc markedly reduced the frequency of mutagenesis in all transfected lines irrespective of transcriptional status. A survey of 17 GPT^- clones derived from two original transfectants showed partial or complete excisions of the transfected gene in every case. These studies show that quantities of cadmium and zinc that induce metallothioneins also suppress the incidence of deletions in murine cells.