Electron Microscopic Observations on the Association of Viruses With Membrane Systems in Hamster Tumor Cells Propagated in Tissue Culture2

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Abstract
Electron microscopic observations on several cell lines derived from hamster tumors, induced by inoculations of Bryan strain Rous sarcoma virus, confirmed the presence of a reovirus (Type III) and indicated two other types of “virus-like” particles. The reovirus was observed in large cytoplasmic viroplasms. Particles with morphology similar to the reovirus particles passed through the outer membrane of mitochondria lying close to the reovirus viroplasms. The particles acquired α membrane envelope in this manner. Particles were not seen in the matrix of the mitochondria. The two other types of virus-like particles observed were 1) α “budding” particle, approximately 155 m/μ in diameter, which originated from electron-dense condensations at the plasma membranes of the cells in vitro, and 2) another budding particle previously described, with radial configuration of internal material that originated from the endoplasmic reticulum. Biologic significance has not been ascribed to these latter two particle types; however, they exhibit the basic criteria for viruses. They appear as accumulations of abnormal or altered protein or nucleoprotein. These observations suggest the possibility of new agents which may be endemic in the hamster.

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