This animation combines data from electron cryo-tomography of intact HIV particles with atomic models of HIV proteins to illustrate the process of HIV maturation. The maturation process is essential for viral transmission and is an important therapy target. Maturation occurs when HIV protease (shown in green) cleaves the Gag polyprotein into its constituent proteins. One of these, the capsid protein (shown in yellow and blue), refolds to form hexameric and pentameric units that construct the mature capsid cone. Exactly how these molecules self-assemble into the larger structure remains unknown; the animation demonstrates one possible pathway.