We have characterized a region of the promoter of a cloned delta9-desaturase gene (Ole1) of Histoplasma capsulatum, a dimorphic pathogenic fungus of humans. The product of the delta9-desaturase gene is involved in regulating membrane fluid state in animal cells and microorganisms. To identify sequences critical for Ole1 expression in both the saprobic mycelial and parasitic yeast phases of this organism, we performed a deletion analysis. Evidence is presented that a 240 nt region of the proximal promoter is involved in a phase-specific binding in vitro. By sequence analysis we have identified one likely regulatory element that coincides with an AP1 binding site (TGACTAA) that is located at -740 nt of 5'-upstream from the ATG. Using gel mobility shift assays, we show that this cis-acting element binds nuclear proteins extracted from the yeast and mycelial phases of H. capsulatum that may participate in control of expression of the delta9-desaturase gene.
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