A system for controlling gene expression in yeast comprises a repressible gene expression plasmid that has a regulator binding sequence for camR and a target gene sequence. The system also includes a transcription enhancer expression plasmid; wherein said transcriptional activator protein binds to the regulator binding sequence in the absence of a transcriptional inhibitor. The system is used in a method for controlling expression of the target gene through the use of camphor. The target gene is expressed in the absence of camphor but unexpressed if camphor is added to a solution of cells containing the plasmids.