When the alkane-assimilating yeast Yarrowia lipolytica is cultivated on n-alkanes, it changes cellular metabolism for adaptation by inducing cytochrome P450 and other genes. From a comparative analysis of promoters of alkane-inducible genes, we identified a cisacting element, ARE1 (alkane responsive element 1), which provides transcription induction in response to n-alkanes. In a genetic selection for mutants that were defective in ARE1-mediated transcription induction in the presence of n-alkanes, we found that the YAS1 (yeast alkane signaling) gene is essential for alkane response. The YAS1 gene encodes a basic helix-loop-helix (bHLH) family protein. Loss of Yas1p causes defects in n-alkanedependent transcription induction of the P450 gene and growth on n-alkanes. Yas1p localizes to nuclei and binds to promoters containing ARE1. Yas1p also binds to its own promoter, and the expression of YAS1 is induced by n-alkanes. These features suggest that Yas1p is a novel transcription factor mediating alkane signaling and that it provides an autoregulatory loop.
The expression of the ALK1 gene, which encodes cytochrome P450, catalyzing the first step of alkane oxidation in the alkane-assimilating yeast Yarrowia lipolytica, is highly regulated and can be induced by alkanes. Previously, we identified a cis-acting element (alkane-responsive element 1 [ARE1]) in the ALK1 promoter. We showed that a basic helix-loop-helix (
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