ELECTRON-MICROSCOPY OF THE NUCLEOCAPSID FROM DISRUPTED MOLONEY MURINELEUKEMIA-VIRUS AND OF ASSOCIATED TYPE-VI COLLAGEN-LIKE FILAMENTS

To analyze the constituents of retroviruses, the Moloney murine leukem ia virus was disrupted and observed by dark-field electron microscopy. Virus disruption was achieved by several methods: osmotic shock, free zing-thawing cycles, and exposure to urea up to 4 M, to NaCl up to 1 M , and to Triton X-100. Several components associated with broken Molon ey murine leukemia virus were repeatedly found in preparations. These components have been described as rings, thick filaments, chain-like f ilaments, threads covered with proteins, threads with buckles, and nak ed threads. A quantitative analysis of the occurrence of these compone nts has been carried out. Among them, the thick filaments composed of a compact helical arrangement of small beads 5 nm in diameter were con sidered to represent the nucleocapsid. The protease-sensitive buckles found on some threads could be a compact form of the viral RNA associa ted to the nucleocapsid protein NCp10. The RNase-sensitive naked threa ds are interpreted as the deproteinized viral RNA itself. The ubiquito us chain-like filaments possess a periodic structure identical to that of polymerized type VI collagen. It is proposed that this adhesive pr otein is associated with the viral envelope taken from the cell membra ne during the budding process of retroviruses.