THE MORPHOLOGY OF THE IMMATURE HIV-1 VIRION

Newly released HIV-1 particles exhibit an immature morphology, previou sly reported to be characterized by a doughnut/ring-shaped structure. In this study we showed that among immature extracellular virus partic les not only were particles with doughnut-shaped morphology present, b ut particles with a crescent morphology were also observed. These part icles occurred with different frequencies, depending on whether they w ere in the cell or in cell-free fractions. The crescent-shaped particl es were more abundant in the cell-free fractions, whereas the particle s in the cell fraction mainly exhibited doughnut-shaped morphology. Th e crescent-shaped structure may represent an assembly intermediate. (C ) 1997 Academic Press.