Molecular cloning and expression of an Erwinia sp. gene encoding diphenyl ether cleavage in Escherichia coli

A 2.1-kilobase fragment obtained by restriction enzyme HindIII digestion of Erwinia sp. genomic DNA was cloned into plasmid pUC19 and introduced into Escherichia coli by transformation. The transformants with diphenyl ether cleaving activity (Dpe+) were selected on agar plates with a specially designed medium (LTFN) containing 4-nitrodiphenyl ether. The positive clones showed a clear zone around the colonies. Analysis of mutants obtained by transposon mini-Mu dI(lacZ Kmr) mutagenesis indicated the coding region of the gene (dpe) and the utilization of a lacZ promoter of pUC19 for transcription of dpe. Clones with dpe in the opposite orientation in pUC19 were not expressed, confirming the need for a lacZ promoter. Utilization of a lacZ promoter in pUC19 was further confirmed by the observation that the degradation of 4-nitrodiphenyl ether was enhanced in the presence of isopropyl-beta-D-thiogalactoside. Expression of dpe was also found in pDPE7321, generated from cloning this gene into another plasmid, pSP73. Analysis of the plasmid-encoded proteins by the maxicell technique showed a polypeptide of 21,000 molecular weight as the product of dpe.