Comparison of selectable and plaque assay systems to detect menadione- and UV-induced lacI mutations in mammalian cells

Abstract

We have compared the spontaneous mutation frequency and spectrum of lacI genes recovered from a rat embryonic fibroblast line transfected with a λ-phage shuttle vector (Rat2λ lacI) using both the traditional plaque assay as well as a positive selection assay. In addition, mutation frequencies and spectrum were determined after treatment of the cells with either the intracellular superoxide-generating compound, menadione, or UVC light. The differences in mutation frequency between the two systems suggested that the selectable assay was better at discerning relatively small mutation frequency increases, more rapidly and at lower cost, than the plaque assay method. Some novel lacI mutations were observed in mutants derived from the selectable assay. This indicates that the selectable assay system may be a useful tool for assessing the mutagenic potential of different agents.