Introduction: The CCAAT sequence is one of cis-elements present in the promoter regions of numerous eukaryotic genes. A statistical analysis revealed that the CCAAT sequence is one of the most common elements that are present in approximately 30% in the eukaryotic promoters. In filamentous fungi, the CCAAT-binding complex (Hap complex), which is homologous to the yeast Hap complex has been characterized extensively. Although the many genes were reported to be regulated by the Hap complex, it is still unclear what category of genes is regulated by the Hap complex. To elucidate the over all picture of the regulatory network, we carried out DNA microarray analyses using Aspergillus oryzae oligonucleotide arrays. Methods: A dominant-negative type mutant hapB gene, which encodes a mutant HapB subunit possessing a lesion in the putative DNA binding domain (hapB-1M) was used, since no deletion mutants of Hap subunit genes of A. oryzae were obtained so far. The transformants of A. oryzae with the mutant gene showed a similar phenotype to the hap deletion mutants of A. nidulans such as poor conidiation. Messenger RNAs from the transformant (designated HapB-1M ) and wild-type A. oryzae strains were prepared and used for the DNA microarray analysis. Results and Discussion: Microarray analysis revealed that not many genes were down-regulated in the HapB-1M strain, unexpectedly. Most of them were categorized as unannotated genes. Together with the fact that CCAAT-boxes are present in promoter regions at a high frequency, it is suggested that the Hap complex mainly enhances the transcription of genes, which are induced only when the genes are under specific conditions. On the other hand, many genes that were up-regulated in the HapB-1M strain were identified. The most remarkable group of genes was that of ribosomal protein genes. Northern analysis with A. oryzae HapB-1M also supported that the Hap complex decrease the amounts of transcripts of ribosomal protein genes. Furthermore, similar results were obtained with an A. nidulans deletion mutant of a Hap subunit gene, indicating that the negative effect of the Hap complex on the ribosomal protein genes is a more general phenomenon, not specific to A. oryzae.
Full conference title:
9th EUROPEAN CONFERENCE ON FUNGAL GENETICS
- ECFG 9th (2008)