EXPRESSION OF THE CEFG GENE IS LIMITING FOR CEPHALOSPORIN BIOSYNTHESIS IN ACREMONIUM-CHRYSOGENUM

The conversion of deacetylcephalosporin C to cephalosporin C is ineffi cient in most Acremonium chrysogenum strains. The cefG gene, which enc odes deacetylcephalosporin C acetyltransferase, is expressed very poor ly in A. chrysogenum as compared to other genes of the cephalosporin p athway. Introduction of additional copies of the cefG gene with its na tive promoter (in two different constructions with upstream regions of 1056 bp and 538 bp respectively) did not produce a significant increa se of the steady-state level of the cefG transcript. Expression of the cefG gene from the promoters of (i) the glyceraldehyde-3-phosphate de hydrogenase (gpd) gene of Aspergillus nidulans, (ii) the glucoamylase (gin) gene of Aspergillus niger, (iii) the glutamate dehydrogenase (gd h) and (iv) the isopenicillin N synthase (pcbC) genes of Penicillium c hrysogenum, led to very high steady-state levels of cefG transcript an d to increased deacetylcephalosporin-C acetyltransferase protein conce ntration (as shown by immunoblotting) and enzyme activity in the trans formants. Southern analysis showed that integration of the new constru ctions occurred at sites different from that of the endogenous cefG ge ne. Cephalosporin production was increased two-to threefold in A. chry sogenum C10 transformed with constructions in which the cefG gene was expressed from the gdh or gpd promoters as a result of a more efficien t acetylation of deacetylcephalosporin C.