title: Regulation of cyclic peptide biosynthesis in a plant pathogenic fungus by a novel transcription factor.
abstract: Strains of the filamentous fungus Cochliobolus carbonum that produce the host-selective compound HC-toxin, a cyclic tetrapeptide, are highly virulent on certain genotypes of maize (Zea mays L.). Production of HC-toxin is under the control of a complex locus, TOX2, which is composed of at least seven linked and duplicated genes that are present only in toxin-producing strains of C. carbonum. One of these genes, TOXE, was earlier shown to be required for the expression of the other TOX2 genes. TOXE has four ankyrin repeats and a basic region similar to those found in basic leucine zipper (bZIP) proteins, but lacks any apparent leucine zipper. Here we show that TOXE is a DNA-binding protein that recognizes a ten-base motif (the "tox-box") without dyad symmetry that is present in the promoters of all of the known TOX2 genes. Both the basic region and the ankyrin repeats are involved in DNA binding. A region of TOXE that includes the first ankyrin repeat is necessary and sufficient for transcriptional activation in yeast. The data indicate that TOXE is the prototype of a new family of transcription factor, so far found only in plant-pathogenic fungi. TOXE plays a specific regulatory role in HC-toxin production and, therefore, pathogenicity by C. carbonum.
authors.affiliation: Department of Energy-Plant Research Laboratory, Michigan State University, East Lansing, MI 48824, USA.
authors.forename: K F
authors.initials: KF
authors.lastname: Pedley
authors.forename: J D
authors.initials: JD
authors.lastname: Walton
mesh_terms: D000595:Amino Acid Sequence; D001203:Ascomycota / Q000235:genetics / Q000378:metabolism*; D001665:Binding Sites; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism* / Q000502:physiology; D005656:Fungal Proteins / Q000235:genetics / Q000378:metabolism* / Q000502:physiology; D005800:Genes, Fungal; D008969:Molecular Sequence Data; D010456:Peptides, Cyclic / Q000096:biosynthesis*; D011401:Promoter Regions, Genetic; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism* / Q000502:physiology; D015533:Transcriptional Activation
chemical_list: D004268:DNA-Binding Proteins; D005656:Fungal Proteins; D010456:Peptides, Cyclic; C116821:TOXE protein, Cochliobolus carbonum; D014157:Transcription Factors; C037654:HC toxin