A Basic Helix-Loop-Helix Transcription Factor Essential for Cytochrome P450 Induction in Response to Alkanes in Yeast Yarrowia lipolytica

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 cis-acting 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-alkane-dependent 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.