Elevation of the Activity of Rate Limiting Enzyme - Cephalosporium aremonium strains are used for the production of cephalosporin C. However, penicillin N, which is an intermediate product in biosynthesis of cephalosporin C, accumulates. Thus the activity of enzyme (encoded in gene cef EF) responsible for converting penicillin N limits the rate of overall pathway.

Expression of cef EF was elevated through increased gene dosage, and the recombinant C. aeremonium exhibited IS-fold reduction in penicillin N concentration and 15% increase in the production of cephalosporin C.