Functional and Structural Dissection of the SWI/SNF Chromatin Remodeling Complex: A Dissertation

The yeast SWI/SNF complex is the prototype of a subfamily of ATP-dependent chromatin remodeling complexes. It consists of eleven stoichiometric subunits including Swi2p/Snf2p, Swi1p, Snf5p, Swi3p, Swp82p, Swp73p, Arp7p, Arp9p, Snf6p, Snf11p, and Swp29p, with a molecular weight of 1.14 mega Daltons. Swi2p/Snf2p, the catalytic subunit of SWI/SNF, is evolutionally conserved from yeast to human cells. Genetic evidence suggests that SWI/SNF is required for the transcriptional regulation of a subset of genes, especially inducible genes. SWI/SNF can be recruited to target promotors by gene specific activators, and in some cases, SWI/SNF facilitates activator binding. Biochemical studies have demonstrated that purified SWI/SNF complex can hydrolyze ATP, and it can use the energy from ATP hydrolysis to generate superhelical torsion, mobilize mononucleosomes, enhance the accessibility of endonucleases to nucleosomal DNA, displace H2A/H2B dimers, induce dinucleosome and altosome formation, or evict nucleosomes. A human homolog of Swi2p/Snf2p, BRG1, is the catalytic subunit of the human SWI/SNF complex. Interestingly, isolated BRG1 alone is able to remodel a mononucleosome substrate. Importantly, mutations in mammalian SWI/SNF core subunits are implicated in tumorigenesis. Therefore, it remains interesting to characterize the role(s) of each subunit for SWI/SNF function. In this thesis project, I dissected SWI/SNF chromatin remodeling function by investigating the role of the SANT domain of the Swi3p subunit. Swi3p is one of the core components of SWI/SNF complex, and it contains an uncharacterized SANT domain that has been found in many chromatin regulatory proteins. Earlier studies suggested that the SANT domain of Ada2p