Abstract: Objective To develop a rapid screening method for chemical mutagens in vitro. Methods RNR3 promoter was amplified using polymerase chain reaction (PCR) from yeast genome and inserted into the yeast report vector of pMP206 / ERE to construct yeast Lac Z gene report vector regulated by RNR3. This vector was transformed into the yeast cell of W303-1A. When the yeast cell was treated by the chemical mutagenesis, the expression of Lac Z gene was induced. So it can be used to screen the chemicals with DNA toxicity by measuring the beta - galactose enzyme activity. Results Various chemicals that cause DNA damaged can induce RNR3 expression. The mutagens alkylating DNA (methyl methanesulfonate and chlorambucil), the cleavages of DNA (cisplatin, 4- nitro -N- oxidation of quinoline, bleomycin and phleomycin) and the inhibitor of DNA polymerase or topoisomerase (5- fluorouracil, hydroxyurea and camptothecin) can induce RNR3 expression. Conclusions The recombinant Lac Z report gene yeast cells regulating by RNR3 can be used for the screening of many chemical mutagen and this screen can be carried out in 96 well micro plate, so it has a high throughput.

Key words: Keywords: mutagens, yeast cells, RNR3 gene, β-galactosidase