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Papers In Press, published online ahead of print March 24, 2008
J. Biol. Chem, 10.1074/jbc.M708683200
Submitted on October 19, 2007
Revised on February 13, 2008
Accepted on March 24, 2008
Bioquimica Y Biologia Molecular, Universidad Autonoma De Barcelona, Cerdanyola, Barcelona 08193
Corresponding Author: JOAQUIN.ARINO{at}UAB.ES
Failure to use glucose as carbon source results in transcriptional activation of numerous genes whose expression is otherwise repressed. HXT2 encodes a yeast high-affinity glucose transporter that is only expressed under conditions of glucose limitation. We show that HXT2 is rapidly and potently induced by environmental alkalinization and this requires both the Snf1 and the calcineurin pathways. Regulation by calcineurin is mediated by the transcription factor Crz1, which rapidly translocates to the nucleus upon high pH stress, and acts through a previously unnoticed Crz1-binding element (CDRE) in the HXT2 promoter (-507 GGGGCTG -501). We demonstrate that, in addition to HXT2, many other genes required for adaptation to glucose shortage, such as HXT7, MDH2 or ALD4, transcriptionally respond to calcium and high pH signaling through binding of Crz1 to their promoters. Therefore, calcineurin-dependent transcriptional regulation appears to be a common feature for many genes encoding carbohydrate-metabolizing enzymes. Remarkably, extracellular calcium allows growth of a snf1 mutant on low glucose in a calcineurin/Crz1 dependent-manner, indicating that activation of calcineurin is sufficient to override a major deficiency in the glucose-repression pathway. We propose that alkalinization of the medium results in impaired glucose utilization and that activation of certain glucose-metabolizing genes by calcineurin contributes to yeast survival under this stress situation.
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