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Molecular and Cellular Biology, July 2006, p. 5470-5480, Vol. 26, No. 14
0270-7306/06/$08.00+0     doi:10.1128/MCB.02443-05
Copyright © 2006, American Society for Microbiology. All Rights Reserved.

Cell Cycle-Dependent Regulation of Saccharomyces cerevisiae Donor Preference during Mating-Type Switching by SBF (Swi4/Swi6) and Fkh1

Eric Coïc, Kaiming Sun, Cherry Wu, and James E. Haber^*

Department of Biology and Rosenstiel Center, Brandeis University, Waltham, Massachusetts 02254-9110

Received 22 December 2005/ Returned for modification 23 February 2006/ Accepted 2 May 2006

Saccharomyces mating-type switching occurs through a double-strand break-initiated gene conversion event at MAT, using one of two donors located distantly on the same chromosome, HML and HMRa. MATa cells preferentially choose HML, a decision that depends on the recombination enhancer (RE) that controls recombination along the left arm of chromosome III. We previously showed that an fhk1 mutation reduces HML usage in MATa cells, but not to the level seen when RE is deleted. We now report that donor preference also depends on binding of the Swi4/Swi6 (SBF) transcription factors to an evolutionarily conserved SCB site within RE. As at other SCB-containing promoters, SBF binds to RE in the G₁ phase. Surprisingly, Fkh1 binds to RE only in G₂, which contrasts with its cell cycle-independent binding to its other target promoters. SBF and Fkh1 define two independent RE activation pathways, as deletion of both Fkh1 and SCB results in nearly complete loss of HML usage in MATa cells. These transcription factors create an epigenetic modification of RE in a fashion that apparently does not involve transcription. In addition, the putative helicase Chl1, previously involved in donor preference, functions in the SBF pathway.

Present address: Whitehead Institute for Biological Research, 9 Cambridge Center, Cambridge, MA 02142.

Present address: Wyeth Research, 401 N. Middletown Road, Pearl River, NY 10965.

This article has been cited by other articles:

• Coic, E., Richard, G.-F., Haber, J. E. (2006). Saccharomyces cerevisiae Donor Preference During Mating-Type Switching Is Dependent on Chromosome Architecture and Organization. Genetics 173: 1197-1206 [Abstract] [Full Text]