NRE, the major nitrogen regulatory protein of Penicillium chrysogenum, binds specifically to elements in the intergenic promoter regions of nitrate assimilation and penicillin biosynthetic gene clusters

Abstract

NRE, the nitrogen regulatory protein of Penicillium chrysogenum, contains a single Cys2/Cys2-type zinc-finger motif followed immediately by a highly basic region. The zinc-finger domain was expressed to Escherichia coli as a fusion protein with β-galactosidase. In order to test the putative DNA-binding ability of NRE, the intergenic promoter region of the nitrate reductase/nitrite reductase gene cluster (niiA-niaD) of Penicillium was sequenced. Our results show that NRE is a DNA-binding protein and binds to the intergenic promoter regions of the P. chrysogenum niiA-niaD and acvA-pcbC gene cluster, encoding the first two enzymes in penicillin biosynthesis. Three of the four high-affinity NRE-binding sites contained two GATA core elements. In one of the recognition sites for NRE, one GATA motif was replaced by GATT. The two GATA elements showed all possible orientations, head-to-head, head-to-tail and tail-to-tail, and were separated by between 4 and 27 bp. Missing-contact analysis showed that all three purines in both of the GATA core sequences and the single adenine residue in each of the complementary TATC sequences were involved in the binding of NRE. Moreover, loss of purines in the flanking regions of the GATA elements also affect binding of NRE, as their loss causes reduced affinity.