THE ASPERGILLUS-NIDULANS ABAA GENE ENCODES A TRANSCRIPTIONAL ACTIVATOR THAT ACTS AS A GENETIC SWITCH TO CONTROL DEVELOPMENT

The Aspergillus nidulans abaA gene encodes a protein containing an ATT S DNA-binding motif and is required for the terminal stages of conidio phore development. Results from gel mobility shift and protection, mis sing-contact, and interference footprint assays showed that AbaA binds to the sequence 5'-CATTCY-3', where Y is a pyrimidine, making both ma jor- and minor-groove contacts. Multiple AbaA binding sites are presen t in the cis-acting regulatory regions of several developmentally cont rolled structural genes as well as those of the upstream regulatory ge ne brl4, the downstream regulatory gene wetA, and abaA itself. These c is-acting regulatory regions confer AbaA-dependent transcriptional act ivation in a heterologous Saccharomyces cerevisiae gene expression sys tem. From these observations, we propose that the AbaA transcription f actor establishes a novel set of feedback regulatory loops responsible for determination of conidiophore development.