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Molecular and Cellular Biology, April 2005, p. 2698-2707, Vol. 25, No. 7
0270-7306/05/$08.00+0     doi:10.1128/MCB.25.7.2698-2707.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.

Promoter Occupancy Is a Major Determinant of Chromatin Remodeling Enzyme Requirements

Archana Dhasarathy and Michael P. Kladde*

Department of Biochemistry and Biophysics, Texas A&M University, College Station, Texas

Received 27 September 2004/ Returned for modification 21 October 2004/ Accepted 3 January 2005

Chromatin creates transcriptional barriers that are overcome by coactivator activities such as histone acetylation by Gcn5 and ATP-dependent chromatin remodeling by SWI/SNF. Factors defining the differential coactivator requirements in the transactivation of various promoters remain elusive. Induction of the Saccharomyces cerevisiae PHO5 promoter does not require Gcn5 or SWI/SNF under fully inducing conditions of no phosphate. We show that PHO5 activation is highly dependent on both coactivators at intermediate phosphate concentrations, conditions that reduce the nuclear concentration of the Pho4 transactivator and severely diminish its association with PHO5 in the absence of Gcn5 or SWI/SNF. Conversely, physiological increases in Pho4 nuclear concentration and binding at PHO5 suppress the need for both Gcn5 and SWI/SNF, suggesting that coactivator redundancy is established at high Pho4 binding site occupancy. Consistent with this, we demonstrate, using chromatin immunoprecipitation, that Gcn5 and SWI/SNF are directly recruited to PHO5 and other strongly transcribed promoters, including GAL1-10, RPL19B, RPS22B, PYK1, and EFT2, which do not require either coactivator for expression. These results show that activator concentration and binding site occupancy play crucial roles in defining the extent to which transcription requires individual chromatin remodeling enzymes. In addition, Gcn5 and SWI/SNF associate with many more genomic targets than previously appreciated.

* Corresponding author. Mailing address: Department of Biochemistry and Biophysics, 2128 TAMU, Texas A&M University, College Station, TX 77843-2128. Phone: (979) 862-6677. Fax: (979) 845-9274. E-mail: kladde{at}tamu.edu.

Molecular and Cellular Biology, April 2005, p. 2698-2707, Vol. 25, No. 7
0022-538X/05/$08.00+0     doi:10.1128/MCB.25.7.2698-2707.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.



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