Eukaryotic Cell doi:10.1128/EC.00412-06
Copyright (c) 2007, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.
bHLH Transcription Factor Heterocomplex of Yas1p and Yas2p Regulates Cytochrome P450 Expression in Response to Alkanes in the Yeast Yarrowia lipolytica
Setsu Endoh-Yamagami,
Kiyoshi Hirakawa,
Daisuke Morioka,
Ryouichi Fukuda,
and
Akinori Ohta*
Department of Biotechnology, The University of Tokyo, Yayoi 1-1-1, Bunkyo-ku, Tokyo, 113-8657, Japan
* To whom correspondence should be addressed. Email:
aaohta{at}mail.ecc.u-tokyo.ac.jp.
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Abstract |
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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 (bHLH) protein, Yas1p, binds to ARE1 in vivo and mediates alkane-dependent transcription induction. Yas1p, however, does not bind to ARE1 by itself in vitro, suggesting that Yas1p requires another bHLH protein partner for its DNA binding, as many bHLH transcription factors function by forming heterodimers. To identify such a binding partner of Yas1p, here we screened ORFs encoding proteins with the bHLH motif from the Y. lipolytica genome database and identified the YAS2 gene. Deletion of the YAS2 gene abolished the alkane-responsive transcription induction of ALK1 and the growth of this yeast on alkanes. We revealed that Yas2p has transactivation activity. Furthermore, Yas1p and Yas2p formed a protein complex that was required for their binding to ARE1. These findings allow us to postulate a model in which bHLH transcription factors Yas1p and Yas2p form a heterocomplex and mediate the transcription induction in response to alkanes.
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