Identification of the pheromone response element inUstilago maydis
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Thea mating type locus ofUstilago maydis contains the structural genes for a pheromone-based cell recognition system that governs fusion of haploid cells. Binding of pheromone to its cognate receptor induces mating competence in haploid cells and stimulates filamentous growth of the dikaryon. We have analyzed transcription of genes located at thea locus and demonstrate that all genes are induced by pheromone. Transcriptional stimulation is mediated by a 9 bp DNA element (ACAAAGGGA) that occurs in multiple copies in both alleles of thea locus. By fusing multimers containing this 9 bp sequence to the pheromone gene promoter and to a heterologous promoter we demonstrate that this sequence acts as a pheromone response element. In addition, we show that expression of theb genes, which regulate pathogenic development of the dikaryon, is also stimulated by pheromone. Pheromone-inducible genes can be divided into three classes depending on whether their expression is reduced, maintained, or increased after cell fusion. These differences may suggest some regulatory cross-talk between thea andb loci.
Key wordsMating type Pheromone response element Signal transduction Gene regulation Ustilago maydis
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