The BRG1 and the Actin Filament System

The DNA in eukaryotic cells is organized with proteins into chromatin. The chromatin structure is dynamic, altered when factors that use DNA as a template need access or to silence regions of the chromosome. The alteration of the chromatin structure is primarily the responsibility of ATP-dependent chromatin-remodeling complexes and histone-modifying complexes. ATP-dependent chromatin-remodeling factors of the SWI/SNF family affect the actin filament orgainzation in the cytoplasm. The SWI/SNF family of chromatin-remodeling complexes is required in transcription of many genes, and the effect on the actin filament organization depends on cell type context, in particular, the various signaling pathways activated in each cell type. In many cell types, SWI/SNF complexes affect the protein level of adhesion molecules and Rho pathway effector molecules. Actin, together with actin-related proteins (ARPs) are also present in the nucleus and are implicated in mRNA export, transcription, DNA repair, and chromatin remodeling. Actin associate to all three types of eukaryotic RNA polymerases (pol). In addition, actin and ARPs are part of several chromatin-remodeling complexes purified from yeast, Drosophila, and mammalian cells. The function of actin and ARPs in the nucleus is still unclear, and it is proposed that they work as motor proteins or as structural proteins in different complexes.