The upstream region of the IPNS gene determines expression during secondary metabolism in Aspergillus nidulans.

We have constructed a translational fusion between the isopenicillin-N-synthetase-encoding gene (IPNS) of Aspergillus nidulans and the lacZ gene of Escherichia coli. Recombinant strains carrying a single copy of the fusion integrated at the IPNS locus produced beta-galactosidase (beta Gal) during secondary metabolism. Integration of the fusion at the argB locus results in a situation in which the only 5'-flanking sequences of the IPNS gene upstream from the chimeric fused gene are those included in the transforming plasmid. Such a strain still expresses beta Gal activity during secondary metabolism, showing that a DNA fragment including sequences of the IPNS gene from nt -2000 to +35 (relative to the translation start codon) still contains sufficient information to drive expression of the fusion gene during secondary metabolism.