CORE SUMMARY The ability to express, purify, characterize, and determine the structures of recombinant HIV-related proteins, RNAs, and their complexes is central to the success of all of our Scientific Projects and Cores. Our Protein Production, Biophysical Characterization, and Structure Determination Core (Core 3) is designed to ensure that all CHEETAH Center members and trainees have access to state-of-the-art instrumentation and expertise in construct design, eukaryotic and bacterial protein expression, biophysical characterization, X-ray crystallography, cryoEM, and training in biophysics and structural biology. Services offered by Core 3 will build on our history of successes in expressing, characterizing, and determining the structures of HIV-related proteins and complexes. Component 1 (Expression and Purification of Proteins and Complexes) will support CHEETAH Center laboratories in the production of proteins needed to gain mechanistic insight into processes important for HIV-1 biology, with potential to inform the development of novel therapeutic approaches. All associated resources are located in the Department of Biochemistry at the University of Utah. Component 2 (Biophysical Characterization) will define and validate the biophysical properties of proteins and complexes produced by CHEETAH Center members using state-of-the-art techniques and instrumentation. These data will provide mechanistic insights, and will support and complement high-resolution structural studies. The associated instrumentation is housed in the Department of Biochemistry at the University of Utah, and experimental design, implementation, and data processing are conducted in collaboration with CHEETAH Center members. This Component will also perform a key training role in our Visiting Scholars Program. Component 3 (Structure Determination) will support CHEETAH Center laboratories by determining structures of proteins and complexes that are important for HIV-1 biology. Structures will be determined by single particle cryoEM or X-ray crystallography, thereby providing a foundation for mechanistic understanding with potential to inform the development of novel therapeutic approaches. This Component will also perform a key training role in our Visiting Scholars Program.