POSITIVE SELECTION FOR DICTYOSTELIUM MUTANTS LACKING URIDINE MONOPHOSPHATE SYNTHASE ACTIVITY BASED ON RESISTANCE TO 5-FLUORO-OROTIC ACID

Whereas transformation of Dictyostelium discoideum now can be done routinely and reliably, there is increasing demand for a system that allows selection of cells that have gone through repeated transformation cycles. Such a system is presented here. Selection is based on resistance to 5-fluoro-orotic-acid (5-FOA). D. discoideum is highly sensitive to this drug, and cells can survive only in the presence of 5-FOA if they carry a defective UMP-synthase gene. After transformation with a plasmid carrying a cloned version of the UMP-synthase gene, 5-FOA resistant cells are obtained at high frequency. Because 5-FOA-resistant cells depend on exogenously added uracil, these cells can be taken through a second round of transformation. A plasmid-borne UMP-synthase gene renders 5-FOA-resistant cells phenotypically ura +. Finally, cells can be further transformed using the standard G418 selection system.