Transcription Activator Interactions with Multiple SWI/SNF Subunits

Abstract

We have previously shown that the yeast SWI/SNF complex stimulates in vitro transcription from chromatin templates in an ATP-dependent manner. SWI/SNF function in this regard requires the presence of an activator with which it can interact directly, linking activator recruitment of SWI/SNF to transcriptional stimulation. In this study, we determine the SWI/SNF subunits that mediate its interaction with activators. Using a photocross-linking label transfer strategy, we show that the Snf5, Swi1, and Swi2/Snf2 subunits are contacted by the yeast acidic activators, Gcn4 and Hap4, in the context of the intact native SWI/SNF complex. In addition, we show that the same three subunits can interact individually with acidic activation domains, indicating that each subunit contributes to binding activators. Furthermore, mutations that reduce the activation potential of these activators also diminish its interaction with each of these SWI/SNF subunits. Thus, three distinct subunits of the SWI/SNF complex contribute to its interactions with activation domains.The yeast SWI/SNF complex alters nucleosome structure in an ATP-dependent reaction, and SWI/SNF activity can lead to the relief of chromatin-mediated repression of transcription (for reviews, see references 30, 50, 64, and 70). SWI/SNF is part of a large family of ATP-dependent chromatin remodeling enzymes, which have been purified and characterized from yeast, Drosophila, Xenopus, and human sources. Yeast SWI/ SNF consists of 11 identified subunits, including a highly conserved ATPase, Swi2/Snf2. A major consequence of SWI/SNF action is the increased accessibility of transcription factors to nucleosomal DNA (10). The complex is able to catalyze the movement of histones along DNA in cis, as well as the displacement of histones from DNA in trans (47,51,68). Recently, it was shown that SWI/SNF generates superhelical torsion within linear DNA fragments and changes in DNA twist, providing a means for the repositioning of nucleosomes along DNA (17,24). Yeast SWI/SNF is able to bind to both DNA and nucleosomes; however, it does so without sequence specificity (9, 52). DNA expression microarray analysis has shown that levels of only a subset (ca. 5%) of yeast genes are affected by the loss of SWI/SNF ATPase activity, including the acid phosphatase and mating-type specific genes (25, 56). Many recent studies have indicated that yeast SWI/SNF and its human counterparts are able to interact with sequence-specific transcription factors, which may recruit the complex to specific genes. A human SWI/SNF complex, E-RC1, functionally and physically interacts with erythroid Krüppel-like factor (EKLF) to increase transcription of the ␤-globin gene (2, 27, 36), and C/EBP␤ interacts with hSWI/SNF to activate myeloid genes (33). Recently, BRG1-containing hSWI/SNF was shown to associate with human heat shock factor 1 (hHSF1) (57). Interactions between SWI/SNF and the glucocorticoid receptor have also been reported (16,45,65,73).Work from our lab and others has shown that purified yeast SWI/S...

Chromatin remodeling by ATP‐dependent molecular machines

“…In addition to the alteration of histone-DNA contacts, chromatin-remodeling factors have been found to function in other chromatin-related processes. For instance, they can facilitate transcription from chromatin templates, (21)(22)(23)(24)(25)(26)(27) catalyze the assembly of periodic nucleosome arrays, (28)(29)(30)(31)(32)(33) and participate in homologous strand pairing. (34,35) Chromatin-remodeling factors-multiple machines with related motors Chromatin-remodeling complexes are compositionally and functionally diverse, yet they share the presence of a motor subunit that belongs to the Snf2-like family of ATPases (36,37) (Fig.…”

“…For example, both the ATPase and non-ATPase subunits of SWI/SNF complexes have been found to be recruited to promoters via interactions with sequence-specific transcription factors (see, for example Refs. 21,24,27).…”

The VP16 Activation Domain Interacts with Multiple Transcriptional Components as Determined by Protein-Protein Cross-linking in Vivo

“…This approach has identified the Tra1 subunit of the SAGA complex (42), several subunits of the Swi/Snf complex (43), and the Srb4 subunit of the mediator complex (44) as direct targets of activation domains in vitro. In the case of Tra1, mutations that * The costs of publication of this article were defrayed in part by the payment of page charges.…”

In vivo target of a transcriptional activator revealed by fluorescence resonance energy transfer

“…The well-characterized acidic activator Gal4 is responsible for the transcriptional stimulation of GAL genes, such as GAL1, which contain Gal4-binding sites in their promoters (Johnston 1987;Johnston and Carlson 1992;Dudley et al 1999). A variety of transcriptional components have been proposed to be the target of Gal4 including TBP (Melcher and Johnston 1995;Wu et al 1996), TFIIB (Wu et al 1996), Srb4 (Koh et al 1998;Park et al 2000), Gal11 (Jeong et al 2001), the Swi/Snf complex (Neely et al 2002), and the SAGA (Spt/Ada/ Gcn5/acetyltransferase) complex (Bhaumik and Green 2001;Brown et al 2001;Larschan and Winston 2001). These proposals are based on either in vitro protein interaction studies or inferences from various indirect in vivo experiments, and to date there is no definitive evidence that Gal4 directly interacts with any of these putative targets in vivo.…”