VERFAHREN ZUR INDUZIERBAREN GENEXPRESSION UNTER VERWENDUNG EINES DHFR-GENS

Disclosed is a method of producing increased amounts of a protein of interest in a cell by induction. The method includes transfecting a cell with multiple copies of an expression vector, each copy of which includes an expressible gene encoding an enzymatically functional dihydrofolate reductase (DHFR) and an expressible gene encoding a protein of interest. Transfected cells are cultured in the presence of methotrexate (MTX) to produce a plurality of clones. A clone containing plural copy number of the vectors which co-express DHFR and the protein of interest is then selected and cultured. The cultured clone is treated with MTX to enhance the expression of the protein of interest by inducing an increase in transcription without substantially amplifying the genes encoding the protein of interest and DHFR.