The modulation of chromatin?structure is an essential?component in?the regulation of transcriptional?activation and repression. Modifications can be made by at least two evolutionarily conserved strategies,through the disruption of histone-DNA?contacts by ATP-dependent chromatin?remodelers,or by histone tail modifications including methylation and acetylation. One of the four classes of ATP-dependent histone remodelers is the SWI/SNF complex,the central catalytic subunit of which is Brg1 or the highly related protein?hBRM. This SWI/SNF complex contains?varying subunits but its association with either Brg1 or hBRM remains constant. SWI/SNF complexes have been shown to regulate?gene activation,cell growth,the cell cycle?and differentiation. Brg1/hBRM?has been shown to regulate?transcription through enhancing transcriptional?activation of glucocorticoid?receptors. Although usually associated with transcriptional?activation,Brg1/hBRM?have also been found in?complexes associated with transcriptional?repression including with HDACs,Rb and Tif1B. Brg1/hBRM?plays a vital role in the regulation of gene transcription during early mammalian embryogenesis. In addition,Brg1/hBRM?also plays a role?as a tumor suppressors and Brg1 is mutated in?several?tumor cell?lines.