AnCF, the CCAAT binding complex of Aspergillus nidulans, contains productsof the hapB, hapC, and hapE genes and is required for activation by the pathway-specific regulatory gene amdR

CCAAT binding factors (CBFs) positively regulating the expression of the am dS gene (encoding acetamidase) and two penicillin biosynthesis genes (ipnA and aatA) have been previously found in Aspergillus nidulans. The factors w ere called AnCF and PENR1, respectively. Deletion of the hapC gene, encodin g a protein with significant similarity to Hap3p of Saccharomyces cerevisia e, eliminated both AnCF and PENR1 binding activities. We now report the iso lation of the genes hapB and hapE, which encode proteins with central regio ns of high similarity to Hap2p and Hap5p of S. cerevisiae and to the CBF-B and CBF-C proteins of mammals. An additional fungus-specific domain present in HapE was revealed by comparisons,vith the homologs from S. cerevisiae, Neurospora crassa, and Schizosaccharomyces pombe. The HapB, HapC, and HapE proteins have been shown to be necessary and sufficient for the formation o f a CCAAT binding complex in vitro. Strains with deletions of each of the h apB, hapC, and hapE genes have identical phenotypes of slow growth, poor co nidiation, and reduced expression of amdS. Furthermore, induction of amdS b y omega amino acids, which is mediated by the AmdR pathway-specific activat or, is abolished in the hap deletion mutants, as is growth on gamma-aminobu tyric acid as a sole nitrogen or carbon source. AmdR and AnCF bind to overl apping sites in the promoters of the amdS and gatA genes. It is known that AnCF can bind independently of AmdR. We suggest that AnCF binding is requir ed for AmdR binding in vivo.