Epoxomicin is an epoxyketone proteasome inhibitor with synthetic derivatives approved or under investigation for treatment of multiple myeloma. To leverage the advantages of Escherichia coli as a rapidly growing and readily engineered host for the production of epoxomicin and analogues, we expressed codon-optimized versions of the epoxomicin biosynthetic genes, epxD, epxE, and epxF. Epoxomicin was detected, but the major product was a ketone resulting from α,β-keto acid precursor decarboxylation. Epoxomicin yield was improved by altering the copy numbers of each gene and creating a fusion of epxE and epxF. Our optimized system offers promise for efficient engineering and biosynthesis of improved epoxomicin analogues.