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Eukaryotic Cell, November 2006, p. 1866-1881, Vol. 5, No. 11
1535-9778/06/$08.00+0     doi:10.1128/EC.00199-06
Copyright © 2006, American Society for Microbiology. All Rights Reserved.

A Transcription Factor Cascade Involving Fep1 and the CCAAT-Binding Factor Php4 Regulates Gene Expression in Response to Iron Deficiency in the Fission Yeast Schizosaccharomyces pombe{triangledown} ,{dagger}

Alexandre Mercier, Benoit Pelletier, and Simon Labbé*

Département de Biochimie, Université de Sherbrooke, Sherbrooke, Québec J1H 5N4, Canada

Received 23 June 2006/ Accepted 31 August 2006

We have identified genes encoding candidate proteins involved in iron storage (pcl1+), the tricarboxylic acid cycle (sdh4+), and iron-sulfur cluster assembly (isa1+) that are negatively regulated in response to iron deprivation. Promoter deletion and site-directed mutagenesis permitted identification of a new cis-regulatory element in the promoter region of the pcl1+ gene. This cis-acting regulatory sequence containing the pentanucleotide sequence CCAAT is responsible for transcriptional repression of pcl1+ under low iron supply conditions. In Schizosaccharomyces pombe, the CCAAT-binding factor is a heteromeric DNA-binding complex that contains three subunits, designated Php2, Php3, and Php5. Inactivation of the php2+ locus negatively affects the transcriptional competency of pcl1+. A fourth subunit, designated Php4, is not essential for the transcriptional activation of target genes under basal and iron-replete conditions. We demonstrate that, in response to iron-limiting conditions, Php4 is required for down-regulation of pcl1+, sdh4+, and isa1+ mRNA levels. In vivo RNase protection studies reveal that the expression of php4+ is negatively regulated by iron and that this regulated expression requires a functional fep1+ gene. The results of these studies reveal that Fep1 represses php4+ expression in response to iron. In contrast, when iron is scarce, Fep1 becomes inactive and php4+ is expressed to act as a regulatory subunit of the CCAAT-binding factor that is required to block pcl1+, sdh4+, and isa1+ gene transcription.

* Corresponding author. Mailing address: Département de Biochimie, Faculté de Médecine, Université de Sherbrooke, 3001 12e Ave. Nord, Sherbrooke, Québec J1H 5N4, Canada. Phone: (819) 820-6868, ext. 15460. Fax: (819) 564-5340. E-mail: Simon.Labbe{at}USherbrooke.ca.

{triangledown} Published ahead of print on 8 September 2006.

{dagger} Supplemental material for this article may be found at http://ec.asm.org/.

Eukaryotic Cell, November 2006, p. 1866-1881, Vol. 5, No. 11
1535-9778/06/$08.00+0     doi:10.1128/EC.00199-06
Copyright © 2006, American Society for Microbiology. All Rights Reserved.



This article has been cited by other articles:

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