ABSTRACT Our Structural Biology Core provides capabilities for visualizing structures of macromolecules, subcellular complexes, cells and tissues. X-ray crystallography (Aim 1) is essential for many of our projects, and has already been used to determine high-resolution structures that yielded insights into HIV architecture and maturation1-3, budding4-11, restriction12,13, immune recognition14-17, and novel therapeutics.18-23 Electron crystallography (Aim 2) will provide structures from 2D crystals, e.g., studies of HIV-1 CA protein26, the CTD- SP1 construct of Gag2 and the TRIM5α restriction factor.27,28 We are also developing methods for electron diffraction from microcrystals29-31, which has considerable potential when large crystals are unavailable, disordered, and/or have packing defects. Electron cryomicroscopy (cryo-EM) and single-particle image reconstruction (Aim 3) are transforming structural biology32, and we have implemented state-of-the-art technology, and previously determined structures that illuminate HIV budding33 and immune recognition.34,35 We have also implemented cutting-edge methods of EM tomography (Aim 4) and applied them to image structures such as authentic viral cores24,36, cores bound by the innate restriction factor TRIM5α28, subcellular structures localized by fluorescence microscopy37, and HIV within tissues.25