Eukaryotic Cell doi:10.1128/EC.00383-06
Copyright (c) 2007, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.
Multiple Basic Helix-Loop-Helix Proteins Regulate Expression of the ENO1 Gene of Saccharomyces cerevisiae
Meng Chen
and
John M. Lopes*
Department of Biological Sciences, Wayne State University, Detroit, Michigan
* To whom correspondence should be addressed. Email:
jlopes{at}sun.science.wayne.edu.
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Abstract |
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The basic helix-loop-helix (bHLH) eukaryotic transcription factors have the ability to form multiple dimer combinations. This property together with the limited DNA-binding specificity to the E-box (CANNTG) makes them ideally suited for combinatorial control of gene expression. We tested the ability of all 9 Saccharomyces cerevisiae bHLH proteins to regulate the enolase-encoding gene, ENO1. ENO1 was known to be activated by the bHLH protein, Sgc1p. Here, we show that expression of an ENO1-lacZ reporter was also regulated by the other 8 bHLH proteins: Ino2p, Ino4p, Cbf1p, Rtg1p, Rtg3p, Pho4p, Hms1p, and Ygr290wp. ENO1-lacZ expression was also repressed by growth in inositol/choline-containing (I+C+) media. Epistatic analysis and Chromatin Immunoprecipitation (ChIP) experiments showed that regulation by Sgc1p, Ino2p, Ino4p, Cbf1p, and repression by inositol/choline required three distal E-boxes: E1, E2, and E3. The pattern of bHLH binding to the 3 E-boxes and experiments with two dominant-negative mutant alleles of INO4 and INO2 support the model that bHLH dimer selection affects ENO1-lacZ expression. These results support the general model that bHLH proteins can coordinate different biological pathways via multiple mechanisms.
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