Purification and characterization of mSin3A-containing Brg1 and hBrm chromatin remodeling complexes

Abstract

Alteration of nucleosomes by ATP-dependent remodeling complexes represents a critical step in the regulation of transcription. The human SWI/SNF (hSWI/SNF) family is composed of complexes that contain either Brg1 or hBrm as the central ATPase; however, these separate complexes have not been compared functionally. Here we describe the establishment of cell lines that express epitope-tagged Brg1 and hBrm and a characterization of the complexes associated with these two ATPases. We show that Brg1 fractionates into two complexes that differ in activity and subunit composition, whereas hBrm is found in one complex with lower activity than the Brg1 complexes. These three complexes can remodel nucleosomal arrays, increase restriction enzyme accessibility, and hydrolyze ATP in a DNA-dependent manner. The three complexes differ markedly in their ability to remodel mononucleosomal core particles. We also show that the hBrm complex and one of the Brg1 complexes contain components of the mammalian Sin3 (mSin3) complex. In addition, we have found that Brg1, hBrm, and BAF155 can interact specifically with mSin3A in vitro, showing a direct association of hSWI/SNF complexes with proteins involved in gene repression. These unexpected functional characteristics indicate that these hSWI/SNF complexes play diverse regulatory roles.

Chromatin Remodeling Complexes Interact Dynamically with a Glucocorticoid Receptor–regulated Promoter

“…Dominant negative BRM was consistently a weaker effector of transcription than dominant negative BRG1 ( Figure 3I). Purified BRM complexes have been previously shown to be weaker chromatin remodelers than purified BRG1 complexes (Sif et al, 2001). This observation along with our results suggested a more pronounced role for BRG1 in the transcriptional process at the MMTV promoter.…”

Mechanisms of ATP dependent chromatin remodeling

“…In Drosophila the two forms of SWI/SNF called BAP (Brahma associated proteins) and PBAP (Polybromo-associated BAP) both contain the same catalytic subunit (Brahma), but are distinguished by BAP containing the OSA subunit and PBAF containing the Polybromo and BAP170 subunits [10]. Although human SWI/SNF can be characterized as being of two forms, namely BAF (BRG1/hBRM-Associated Factors) and PBAF (Polybromo-associated BAF), there are many forms of human SWI/SNF that acquire tissue-specific subunits [11] or additional sub-complexes in which the SWI/SNF-type remodelers are associated with other factors such as BRCA1 [12,13], components of the histone deacetylase Sin3 complex [14] and histone methylases [15,16]. Recently, Rtt102p was identified as the newest subunit of both SWI/SNF and RSC complexes by MudPIT or mass spectrometry analysis [17].…”

The requirement for SNF5/INI1 in adipocyte differentiation highlights new features of malignant rhabdoid tumors

“…They play a major role in transcription regulation through physical and functional interactions with transcriptional activators or repressors (Sif et al, 2001) and are involved in a variety of cellular processes, including the regulation of cell growth and differentiation (Roberts and Orkin, 2004). In particular, SWI/ SNF-mediated chromatin remodeling is essential for the myeloid, erythropoietic, adipogenic, neuronal or myogenic differentiation pathways (de la Serna et al, 2006).…”