Overview
In order to create a circle-zero derivative from a Cir+ strain, the method of Rose and Broach (1990) is used. A 2-micron-based plasmid, YEp351-GAL-FLP1 *, that carries the LEU2 selectable marker and also the FLP1 gene under the control of the GAL promoter is transformed into yeast. Leu+ transformants are grown on medium containing galactose as the carbon source. Under these conditions, the FLP1 gene is overexpressed and causes over-replication of the endogenous and artificial 2-micron plasmids, which is deleterious to cells. Therefore, cells that have lost the plasmids have a significant growth advantage over those that retain them.
Details
Details of this protocol, Curing Strains Of Endogenous 2-Micron Plasmid, are located on a web site other than Biocompare Protocols.