The Tan laboratory is interested in how genes are regulated in eukaryotic cells. We are particularly interested in the structural interactions that enable macromolecules to assemble into gene regulatory complexes, and how such regulatory complexes control transcription. We use biochemical and X-ray crystallographic methods to address (1) how a limited number of transcription factors can interact in a combinatorial fashion with different results, and what structural features are involved in such protein-protein or protein-DNA interactions, and (2) how large histone acetylation complexes such as the SAGA complex are assembled and recruited to gene promoters to activate transcription.