Transcriptional regulation through chromatin requires the concerted activity of multisubunit enzymes that chemically modify or structurally remodel nucleosomes. A critical issue is how such diverse complexes are targeted to specific promoters to regulate appropriate patterns of gene expression. This proposal focuses on the well-characterized SWI/SNF family of chromatin remodeling enzymes. Mammalian SWI/SNF exists in biochemically distinct forms that can be divided into two major classes depending upon which ATPase catalytic subunit, BRG1 or BRM, is present. Using a biochemical approach with chromatin-assembled genes we find that SWI/SNF-BRG1 complexes are recruited in a promoter-selective manner by preferential interactions with certain classes of transcription factors. We have recently identified interactions with other proteins and chromatin modifying enzymes that are key components of critical cellular pathways. Interestingly, these proteins preferentially associate with distinct forms of SWl/SNF. The goal of this proposal is to define the specialized functional roles of BRG1- and BRM-containing SWI/SNF complexes in gene regulation and the mechanisms by which they occur. Our experimental design includes a combination of in vitro biochemical and cell-based approaches: protein-protein and protein-chromatin interactions, transcription of nucleosomal templates, chromatin immunoprecipitation, and genome-wide location analyses of distinct SWI/SNF complexes. Mutations in individual SWI/SNF subunits are found in many human cancers. A better understanding of how SWI/SNF is normally recruited to specific genes should provide valuable insight into how mutated forms may contribute to transcriptional deregulation by promoter mistargeting.
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