Oleate induces the transcription of genes involved in peroxisome biogenesis and stimulates the proliferation of these organelles in Saccharomyces cerevisiae. Previously, we have reported the identification of a region containing a positive regulatory element in the 5′ flanking region of the FOX3 gene encoding the peroxisomal enzyme 3‐oxoacyl‐CoA thiolase. This region contains a 23‐bp imperfect inverted‐repeat sequence. Full induction, in response to oleate, is mediated by the intact dyad. However, one half‐site of the inverted repeat is also able to mediate induction of transcription in response to oleate, albeit to a small extent. Furthermore, the weak binding of protein to each part of the inverted repeat proved to be correlated with the weak activation of transcription, in support of oleate. A DNase‐I footprint covered the entire dyad and DNA band‐shift experiments indicated that one or more trans‐acting factors bind to the imperfect palindrome. The binding of protein to this element seems to be correlated with transcriptional activation, since mutations in both halves of the inverted dyad affected both transcriptional activation and protein binding in vitro. Similar oleate‐responsive elements are commonly found in the 5′ flanking regions of genes encoding proteins involved in peroxisome biogenesis and the factor(s) binding to oleate‐responsive element(s) could therefore be involved in coordination of the expression of oleate‐inducible genes and the proliferation of peroxisomes.

Expression of the FOX3 gene, which encodes yeast peroxisomal 3-oxoacyl-coenzyme A thiolase, can be induced by oleate and repressed by glucose. Previously, we have shown that induction was mediated by an oleate response element. Just upstream of this element a negatively acting control region that mediated glucose repression was found. In order to study this negative control region, we carried out DNA-binding assays and analyzed phenotypes of mutations in this region and in the trans-acting factor CAR80, which is identical to UME6. DNA-binding assays showed that two multifunctional yeast proteins, ABF1 and RP-A, interacted with the negative control element independently of the transcriptional activity of the FOX3 gene. ABF1 and RP-A, the latter being identical to BUF, were able to bind to DNA independently of one another but also simultaneously. The phenotypes of mutations in either DNA-binding sites of ABF1, RP-A, or both, which affected the DNA binding of these factors in vitro, indicated that these sites and the proteins that interact with them participate in glucose repression. The involvement of the RP-A site in glucose repression was further supported by our observation that the CAR80 gene product, which is required for repression mediated by the RP-A site, was essential for maintenance of glucose repression. In addition to the RP-A site in the FOX3 promoter, similar sequences were observed in other genes involved in peroxisomal function. RP-A proved to bind to all of these sequences, albeit with various affinities. From these results it is concluded that the ABF1 and RP-A sites are being required in concert to mediate glucose repression of the FOX3 gene. In addition, coordinated regulation of expression of genes involved in peroxisomal function in response to glucose is mediated by proteins associated with the RP-A site, probably RP-A and CAR80.

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