A gene cluster in Aspergillus nidulans with an internally located cis-acting regulatory region.

Work reported here on the fungus Aspergillus nidulans has provided the first definitive demonstration of operon-type organisation in an eukaryote genome. It has been shown that the prnA and prnB genes concerned with proline metabolism form a gene cluster with the regulatory region lying between the two putative structural genes prnA and prnB. Regulatory mutations (prnd) probably leading to relief of carbon catabolite repression, map in between prnA and prnB and are cis-dominant with respect to both. The properties of these regulatory mutations and other findings suggest that carbon catabolite repression may be mediated by a negative control system in A. nidulans. This gene cluster is particularly interesting in view of its divergent orientation (with the regulatory region located in the centre of the operon) and for the fact that unlike the divergent operons known in prokaryotes, the divergent orientation is related to the way in which this particular operon may be regulated.