In situ chromatin dynamics and HIV-1 nuclear trafficking.

The organization and dynamics of chromatin within intact nuclei remain poorly defined, limiting understanding of how nuclear architecture influences macromolecular transport. HIV-1 provides a striking example of a large complex that must traverse this dynamic landscape to access integration sites within transcriptionally active regions. Here, we combine a functional nuclear import system with correlative cryo-electron tomography to visualize chromatin architecture and HIV-1 cores in situ during nuclear penetration. Native nucleosomes resolved at 5.6 Å reveal four structural classes, from compact conformations at the nuclear periphery to open, flexible forms in the interior, defining a spatially heterogeneous and dynamic chromatin landscape. Within this environment, HIV-1 cores decorated with nuclear factors exclude nearby nucleosomes and preferentially associate with open chromatin. Disruption of CPSF6-capsid interactions abolishes these associations, confining viral cores to peripheral chromatin. These findings establish an in situ framework linking chromatin structure and dynamics to HIV-1 nuclear trafficking and provide a structural basis for viral navigation within the dynamic nuclear landscape.