by Karl Bayer, Monika Cserjan-Puschmann, Reingard Grabherr, Gerald Striedner, and Franz Clementschitsch, Institute of Applied Microbiology, Vienna, Austria A new strategy for controlling recombinant gene expression improves efficiency, maximizes host vector exploitation, reduces costs, improves product consistency, and accelerates product development. Continuous feeds of limited amounts of inducer proportional to biomass growth grant optimal control over the ratio between gene expression and host cell metabolism, providing stable, prolonged recombinant protein production.