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Molecular and Cellular Biology, February 2008, p. 1393-1403, Vol. 28, No. 4
0270-7306/08/$08.00+0     doi:10.1128/MCB.01733-07
Copyright © 2008, American Society for Microbiology. All Rights Reserved.

Spn1 Regulates the Recruitment of Spt6 and the Swi/Snf Complex during Transcriptional Activation by RNA Polymerase II ^,

Lei Zhang,^1, Aaron G. L. Fletcher,¹ Vanessa Cheung,² Fred Winston,² and Laurie A. Stargell^1*

Department of Biochemistry and Molecular Biology, Colorado State University, Fort Collins, Colorado 80523,¹ Department of Genetics, Harvard Medical School, Boston, Massachusetts 32003²

Received 20 September 2007/ Returned for modification 12 October 2007/ Accepted 27 November 2007

We investigated the timing of the recruitment of Spn1 and its partner, Spt6, to the CYC1 gene. Like TATA binding protein and RNA polymerase II (RNAPII), Spn1 is constitutively recruited to the CYC1 promoter, although levels of transcription from this gene, which is regulated postrecruitment of RNAPII, are low. In contrast, Spt6 appears only after growth in conditions in which the gene is highly transcribed. Spn1 recruitment is via interaction with RNAPII, since an spn1 mutant defective for interaction with RNAPII is not targeted to the promoter, and Spn1 is necessary for Spt6 recruitment. Through a targeted genetic screen, strong and specific antagonizing interactions between SPN1 and genes encoding Swi/Snf subunits were identified. Like Spt6, Swi/Snf appears at CYC1 only after activation of the gene. However, Spt6 significantly precedes Swi/Snf occupancy at the promoter. In the absence of Spn1 recruitment, Swi/Snf is constitutively found at the promoter. These observations support a model whereby Spn1 negatively regulates RNAPII transcriptional activity by inhibiting recruitment of Swi/Snf to the CYC1 promoter, and this inhibition is abrogated by the Spn1-Spt6 interaction. These findings link Spn1 functions to the transition from an inactive to an actively transcribing RNAPII complex at a postrecruitment-regulated promoter.

Published ahead of print on 17 December 2007.

Supplemental material for this article may be found at http://mcb.asm.org/.

Present address: Department of Dermatology, School of Medicine, University of Colorado Health Sciences Center, Aurora, CO 80045.