Novel basic-region helix-loop-helix transcription factor (AnBH1) of Aspergillus nidulans counteracts the CCAAT-binding complex AnCF in the promoter of a penicillin biosynthesis gene.
Cis-acting CCAAT elements are found frequently in eukaryotic promoter regions. Many of the genes containing such elements in their promoters are regulated by a conserved multimeric CCAAT-binding complex. In the fungus Emericella (Aspergillus) nidulans, this complex was designated AnCF (A.nidulans CCAAT-binding factor). AnCF regulates several genes, including the penicillin biosynthesis genes ipnA and aatA. Since it is estimated that the CCAAT-binding complex regulates more than 200 genes, an important question concerns the regulation mechanism that allows so many genes to be regulated by a single complex in a gene-specific manner. One of the answers to this question appears to lie in the interaction of AnCF with other transcription factors. Here, a novel transcription factor designated AnBH1 was isolated. The corresponding anbH1 gene was cloned and found to be located on chromosome IV. The deduced AnBH1 protein belongs to the family of basic-region helix-loop-helix (bHLH) transcription factors. AnBH1 binds in vitro as a homodimer to an, not previously described, asymmetric E-box within the aatA promoter that overlaps with the AnCF-binding site. This is the first report demonstrating that the CCAAT-binding complex and a bHLH transcription factor bind to overlapping sites. Since deletion of anbH1 appears to be lethal, the anbH1 gene was replaced by a regulatable alcAp-anbH1 gene fusion. The analysis of aatAp-lacZ expression in such a strain indicated that AnBH1 acts as a repressor of aatA gene expression and therefore counteracts the positive action of AnCF.
Caruso
Maria Louise
ML
Institut für Mikrobiologie, Universität Hannover, Schneiderberg 50, 30167 Hannover, Germany.
Litzka
Olivier
O
Martic
Goran
G
Lottspeich
Friedrich
F
Brakhage
Axel A
AA
D000595:Amino Acid Sequence; D001233:Aspergillus nidulans / Q000235:genetics* / Q000378:metabolism; D001665:Binding Sites; D023081:CCAAT-Binding Factor / Q000235:genetics / Q000378:metabolism*; D004247:DNA / Q000378:metabolism; D019281:Dimerization; D005656:Fungal Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D015966:Gene Expression Regulation, Fungal; D005800:Genes, Fungal / Q000235:genetics*; D017930:Genes, Reporter; D018257:Helix-Loop-Helix Motifs; D008969:Molecular Sequence Data; D010406:Penicillins / Q000096:biosynthesis; D011401:Promoter Regions, Genetic; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D012097:Repressor Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D016415:Sequence Alignment; D014157:Transcription Factors / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*
D023081:CCAAT-Binding Factor; D005656:Fungal Proteins; D010406:Penicillins; D011993:Recombinant Fusion Proteins; D012097:Repressor Proteins; D014157:Transcription Factors; D004247:DNA