Isolation and developmentally regulated expression of an Aspergillus nidulans phenol oxidase-encoding gene, ivoB.

Ivory (ivo) mutants of Aspergillus nidulans lack conidiophore pigmentation. We have cloned ivoB which codes for a conidiophore-specific phenol oxidase (AHTase) via the adjacent selectable ureD gene. Gene-library transformants of a ureD4 strain proved defective for the vector, but we recovered both ureD and ivoB from a lambda library of transformant DNA. The ivoB transcription unit was localized to a SalI-XbaI 3-kb fragment and its 5' end was located by hybridization with an oligodeoxyribonucleotide corresponding to the N-terminal polypeptide sequence of AHTase. Expression of the ivoB 1.4-kb mRNA corresponded temporally with AHTase in conidiating cultures, and the levels of both mRNA and AHTase in leaky brlA mutants implied transcriptional control by brlA. A second developmentally regulated locus of unknown function adjacent to ivoB was also transcriptionally dependent on brlA, but was expressed 4 h later.