A method of producing a protein of interest (POI) by culturing a recombinant eukaryotic cell line comprising an expression construct comprising a regulatable promoter and a nucleic acid molecule encoding a POI under the transcriptional control of said promoter, comprising the steps a) cultivating the cell line with a basal carbon source repressing the promoter, b) cultivating the cell line with a limited amount of a supplemental carbon source de-repressing the promoter to induce production of the POI at a transcription rate of at least 15% as compared to the native pGAP promoter, and c) producing and recovering the POI; and further an isolated regulatable promoter and a respective expression system.