ThehapC gene ofAspergillus nidulans is involved in the expression of CCAAT-containing promoters

The 5′ regulatory region of theamdS gene ofAspergillus nidulans, which encodes an acetamidase required for growth on acetamide as a carbon and nitrogen source, contains a CCAAT sequence which is required for setting the basal level ofamdS expression. Mobility shift studies have identified a factor inA. nidulans nuclear extracts which binds to this CCAAT sequence. InSaccharomyces cerevisiae theHAP3 gene encodes one component of a multisubunit complex that binds CCAAT sequences. A search of the EMBL and SwissProt databases has revealed anA. nidulans sequence with significant homology to theHAP3 gene adjacent to the previously cloned regulatory geneamdR. Sequencing of the remainder of this region has confirmed the presence of a gene, designatedhapC, with extensive homology toHAP3. The predicted amino acid sequence of HapC shows extensive identity to HAP3 in the central conserved domain, but shows little conservation in the flanking sequences. A haploid carrying ahapC deletion has been created and is viable, but grows poorly on all media tested. This null mutant grows especially slowly on acetamide as a sole carbon and nitrogen source, indicating thathapC plays a role inamdS expression. In agreement with this notion, it has been shown that thehapC deletion results in reduced levels of expression of anamdS::lacZ reporter gene and this effect is particularly evident under conditions of carbon limitation. Nuclear extracts prepared from thehapC deletion mutant show no CCAAT binding activity to theamdS orgatA promoters, indicating thathapC may encode a component of the complex binding at this sequence.