The cores of human and simian immunodeficiency viruses (HIV and SIV) were observed by negative staining after isolation of the core with Nonidet P40 and glutaraldehyde. Four kinds of cores were found: asymmetric and symmetric sectoral shapes, a bar shape, and a triangular shape. These results were confirmed by the examination of ultrathin sections of whole virions. In some virions, the connection between the core and the envelope was observed after freeze fracturing. Its structure was considered to be characteristic of an intermediate stage of viral maturation. The HIV-1 core was reacted with anti-HIV-1 p24 mouse monoclonal antibody.

Abstract. Cores of human immunodeficiency virus type 1 (HIV-i) were observed using negative staining for electron microscopy. On the surfaces of cores isolated from viral particles with a Nonidet P40 and glutaraldehyde mixture, mortar-like units were detected in the wide and narrow margins. In some of the cores which were burst with distilled water, the units were linked together revealing a beaded structure.