The expression of cytochrome P450IIB1 in Saccharomyces cerevisiae results in an increased mutation frequency when exposed to cyclophosphamide.

A recombinant plasmid containing a full length cDNA encoding the rat cytochrome P450IIB1 under the control of the Saccharomyces cerevisiae ADC1 promoter was constructed and transformed into the yeast strain KY118. The encoded P450IIB1 protein was produced at a level of between 0.1 and 0.2% of total yeast cellular protein (0.068 nmol/mg total cellular protein). This protein was localized in the microsomal fraction and had activity towards the substrate benzyloxyresorufin, the activity being 0.16 nmol resorufin produced/min/mg microsomal protein. When exposed to the anticancer drug cyclophosphamide the mutation frequency, as determined by the development of resistance to the arginine analogue canavanine, increased in a dose-dependent manner over a control strain and was up to 16-fold higher at the highest doses used.