Vinblastine and vincristine are two medically important bisindole alkaloids from Catharanthus roseus (Madagascar periwinkle). Attempts at production in cell cultures failed because a part of the complex pathway was not active, i.e. from tabersonine to vindoline. It starts with tabersonine 16-hydroxylase (T16H), a cytochrome P450-dependent enzyme. We now show that T16H is induced in the suspension culture by light and we report the cloning of the cDNA. The enzyme was expressed in Escherichia coli as translational fusion with the P450 reductase from C. roseus, and the reaction product was identified by mass spectrometry. The protein (CYP71D12) shares 47^52% identity with other members of the CYP71D subfamily with unknown function. The induction by light was strongly enhanced by a nutritional downshift (transfer into 8% aqueous sucrose). We discuss the possibility that the entire pathway to bisindoles can be expressed in suspension cultures.z 1999 Federation of European Biochemical Societies.