Improved expression of a hybrid Streptomyces clavuligerus cefE gene in Penicillium chrysogenum

A hybrid cefE gene, encoding penicillin N expandase, was constructed by fusing the promoter sequences, Pcp, and terminator sequences, Pct from the Penicillium chrysogenum pcbC gene to the open reading frame (orf), cefEorf, from the Streptomyces clavuligerus cefE gene. The resulting hybrid gene, Pcp/cefE'orf/Pct, differed from a previously reported hybrid cefE gene contained on plasmid pPS65. The latter gene, Pcp/cefE'orf/Sct, contained the Pcp sequences fused to the S. clavuligerus cefE orf still attached to the S. clavuligerus terminator sequences, Sct. The new hybrid gene was transformed into P. chrysogenum on plasmid vector pRH6. Transformants were selected by phleomycin resistance conferred by a hybrid ble gene present on plasmid pRH6. The hybrid ble gene was formed by attaching Pcp sequences to the ble orf. Among transformants obtained with pRH6, one exhibited a 70-fold higher level of activity of penicillin N expandase than the best transformant previously obtained from a 10-fold larger population of pPS65 transformants. The penicillin N expandase activity in pRH6 transformant, 9EN-5-1, was fourfold higher than the activity in the S. clavuligerus strain used as the source of the cefE orf and 75% of the activity observed in an industrial strain of Cephalosporium acremonium. Sequencing of the junctions of the heterologous DNA in Pcp/cefEorf/Pct uncovered a modification of the cefE open reading frame introduced during construction of the hybrid gene; the modified open reading frame is designated cefE'orf.