Expression of the Aspergillus nidulans argB gene in Escherichia coli

The Aspergillus nidulans argB gene coding for ornithine carbamoyltransferase (OTCase) is not expressed in Escherichia coli. However, E. coli OTCase-deficient strains transformed with plasmids carrying the argB gene from A. nidulans reverted to prototrophy at a high frequency. In these derivatives the argB gene became functional due to DNA rearrangements upstream of the coding sequence. Two types of rearrangement were characterized. One was identified as an insertion of IS2. The second was a deletion that resulted in transcription of the argB gene from the TcR gene promoter and translation from a newly created ribosome-binding site formed at the junction between the A. nidulans and vector DNA sequences.