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

We have compared the spontaneous mutation frequency and spectrum of lacI ge nes recovered from a rat embryonic fibroblast line transfected with a lambd a-phage shuttle vector (Rat2 lambda lacI) using both the traditional plaque assay as well as a positive selection assay. In addition, mutation frequen cies 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 tha t the selectable assay was better at discerning relatively small mutation f requency increases, more rapidly and at lower cost, than the plaque assay m ethod. 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. (C) 1999 Elsevier Science B.V. All rights reserved.