PROJECT SUMMARY The HIV-1 capsid provides a protective conical enclosure for the transport of the viral genome to its integration sites inside the nucleus. The capsid must uncoat to release the newly formed vDNA and to establish a permanent infection of target cells. When? where? and how? capsids are uncoated remain unclear and hotly debated in the field. This is especially relevant, as new highly active antiretrovirals such as the clinically approved drug Lenacapavir are being developed to combat virus infection. For infection to proceed, the core must cross the nuclear pore complex (NPC) to deliver the viral DNA (vDNA) to integration sites in the nucleus. This process requires structural remodeling of the capsid, which adapts through elastic deformation to penetrate the NPC’s ~64 nm channel. However, the mechanisms underlying capsid remodeling remain poorly understood. My preliminary evidence suggests that the phase separation properties of the host factor CPSF6 stabilize capsid structures in vitro and facilitates capsid trafficking in the nucleus of living cells to nuclear speckles, which are actively transcribing chromatin compartments favored for HIV-1 integration. Disruption of these processes, including with capsid-targeting drugs, impairs nuclear entry and viral infectivity, highlighting their biological relevance. This proposal has two specific aims. AIM-1 will resolve how CPSF6 influences HIV-1 capsid morphology in vitro. Using affinity captured virus particles, correlative light and electron microscopy (CLEM), and cryo-electron tomography (cryo-ET), I will reconstruct CPSF6-bound capsid structure and test the morphological adaptations of the HIV-1 core by host-factor interactions. AIM-2 will extend these findings to infected cells. I will use live-cell imaging, and a CLEM-guided cryo-focused ion beam milling (FIB) of cells and cryo-ET of a lamella prepared at the location of HIV-1 cores to capture capsid structures at multiple stages of entry, from the cy