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J Biol Chem. 2009 Feb 13;284(7):4422-8. doi: 10.1074/jbc.M808263200. Epub 2008 Dec 4.

Mediator subunit Gal11p/MED15 is required for fatty acid-dependent gene activation by yeast transcription factor Oaf1p.

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Massachusetts General Hospital Cancer Center and the Department of Cell Biology, Harvard Medical School, Charlestown, Massachusetts 02129, USA.


The yeast zinc cluster transcription factor Oaf1p activates transcription of target genes in response to direct binding of fatty acids in a manner analogous to the vertebrate nuclear receptor peroxisome proliferator-activated receptoralpha (PPARalpha). PPARs and other metazoan nuclear receptors productively engage several distinct LXXLL motif-containing co-activators, including p160 family members and the TRAP220/MED1 subunit of the Mediator co-activator, to promote ligand-dependent gene activation. Yeast, however, does not appear to harbor LXXLL motif co-activators, and the mechanism of fatty acid-dependent gene activation by the yeast PPARalpha analog Oaf1p is unknown. Here we show that the yeast Mediator subunit Gal11p/MED15 and its activator-targeted KIX domain plays a critical role in fatty acid-dependent transcriptional regulation of fatty acid beta-oxidation and peroxisomal genes by Oaf1p and for the ability of yeast to utilize fatty acids as a sole carbon source. Moreover, structural studies by NMR spectroscopy reveal that the Oaf1p activation domain interacts with the Gal11p/MED15 KIX domain in a manner similar to the yeast zinc cluster family member and xenobiotic receptor Pdr1p, revealing that the Gal11p/MED15 KIX domain is a key target of several ligand-dependent transcription factors in yeast. Together with previous work showing that the Caenorhabditis elegans Gal11p/MED15 homolog MDT-15 plays a critical role in regulation of fatty acid metabolism by the nematode PPAR-like nuclear receptor NHR-49, the findings presented here provide evidence for an ancient and essential role of a Mediator co-activator subunit in regulation of fatty acid metabolism by nuclear receptor-like transcription factors in eukaryotes.

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