The Lysobacter lactamgenus YK90 pcbC gene encoding isopenicillin N synthase (IPNS) was cloned using the corresponding Acremonium chrysogenum pcbC gene as a probe. The cloned pcbC gene encoded a polypeptide composed of 326 amino acid residues with a molecular weight of 36,562, The predicted amino acid sequence had a high similarity with those from fungus A. chrysogenum and actinomycetes Streptomyces clavuligerus. The pcbC gene was expressed in E. coli and in A. chrysogenum under control of the tac and GAP promoters, respectively.