Components of the Human SWI/SNF Complex Are Enriched in Active Chromatin and Are Associated with the Nuclear Matrix

Abstract

Biochemical and genetic evidence suggest that the SWI/SNF complex is involved in the remodeling of chromatin during gene activation. We have used antibodies specific against three human subunits of this complex to study its subnuclear localization, as well as its potential association with active chromatin and the nuclear skeleton. Immunofluorescence studies revealed a punctate nuclear labeling pattern that was excluded from the nucleoli and from regions of condensed chromatin. Dual labeling failed to reveal significant colocalization of BRG1 or hBRM proteins with RNA polymerase II or with nuclear speckles involved in splicing. Chromatin fractionation experiments showed that both soluble and insoluble active chromatin are enriched in the hSWI/SNF proteins as compared with bulk chromatin. hSWI/SNF proteins were also found to be associated with the nuclear matrix or nuclear scaffold, suggesting that a fraction of the hSWI/SNF complex could be involved in the chromatin organization properties associated with matrix attachment regions.

SWI/SNF: The crossroads where extracellular signaling pathways meet chromatin

“…This view of the nuclear organization is congruent with the finding that components of the human SWI/SNF complex are enriched in active chromatin and are associated with the nuclear matrix (Reyes et al, 1997). As such, it will be interesting to define the role of G-actin in the SWI/SNF complex, and to identify the molecules forming the ''nuclear-skeleton'' that sustains the nuclear architecture.…”

“…These molecular events result in the reversible inactivation of SWI/SNF activity and the displacement of the remodeling complexes from the condensed chromatin (Muchardt et al, 1996;Reyes et al, 1997;Sif et al, 1998). To date, it is not clear which kinases are responsible for the phosphorylation of SWI/SNF subunits in vivo, and which phosphatases are required for reactivating dephosphorylation at the beginning of the G1 phase of the cell cycle.…”

Hyperphosphorylation of RNA Polymerase II in Response to Topoisomerase I Cleavage Complexes and Its Association with Transcription- and BRCA1-dependent Degradation of Topoisomerase I

“…This treatment released chromatin-associated proteins almost completely, 55 including the transcribing Pol IIo. 56 The remaining chromatin-associated proteins in the pellet were further extracted with 2 M NaCl in CSK buffer for 15 min at 4°C and centrifugated at 20,000 × g for 15 min. The remaining pellet was solubilized in buffer containing 1% SDS, 1 mM sodium vanadate, 10 mM Tris-HCl, pH 7.4, supplemented with protease and phosphatase inhibitors and was considered the nuclear matrix-containing fraction.…”

Human Arf tumor suppressor specifically interacts with chromatin containing the promoter of rRNA genes

“…To address this point, we carried out experiments to distinguish the so-called active and inactive chromatin parts, before separating them by sucrose-gradient fractionation, according to the protocol published by Arnan et al (2003) with minor modifications. This method, consisting of a mild digestion of nuclei by the micrococcal nuclease, relies on biochemical studies showing that transcriptionally active chromatin exhibits increased sensibility to nucleases (Rose and Garrard, 1984;Reyes et al, 1997). Nuclei were isolated from H-358 or 293 cells.…”