Representatives of three families of enveloped viruses were shown to fuse tissue culture cells together. These were: Semliki Forest virus (SFV, a togavirus), vesicular stomatitis virus (a rhabdovirus), and two myxoviruses, fowl plaque virus and Japan influenza virus (Japan)/A/305/57). Unlike paramyxoviruses, whose fusion activity is known to occur over a broad pH range, fusion by these viruses was restricted to mildly acidic pH. The pH thresholds for the four viruses were 6.0, 6.1, 5.5, and 5.1, respectively. The precursor form of Japan influenza, which is not infectious and which contains the uncleaved hemagglutinin, had no fusion activity. This result suggested a role for the influenza hemagglutinin in the low-pH-dependent membrane fusion activity. Taken together, our results show that low-pH-induced fusion is a widespread property of enveloped animal viruses and that it may play a role in the infective process. The fusion reactions with all four viruses were fast, efficient, and easy to induce. With UV-inactivated SFV, the fusion was shown to be nonlytic and the polykaryons were viable for at least 12 h. 30 ng of SFV/1 x 10(6) BHK-21 cells were required for 50% fusion, and 250 ng sufficed to fuse the entire culture into a single polykaryon.

https://rupress.org/jcb/article-pdf/89/3/674/1074809/674.pdf

Cell fusion by Semliki Forest, influenza, and vesicular stomatitis viruses.

Observations additional to those previously reported (34) on boutons terminaux and club endings on Mauthner cell lateral dendrites, primarily as seen in sections of permanganate-fixed material, are described. Certain new findings on OSO4-fixed endings are also included. The boutons terminaux are closely packed in the synaptic bed with ∼ 100 to 150 A gaps between their contiguous unit membranes and a few interspersed glial extensions. Their synaptic membrane complexes (SMC) appear as pairs of unit membranes separated by ∼ 100 to 150A clefts. They contain many vesicles and unoriented mitochondria, but no neurofilaments. The club endings after KMnO4 fixation are, as after OSO4 fixation (34), again seen surrounded by a layer of extracellular matrix material. These endings contain relatively few synaptic vesicles, a few unit membrane limited tubules ∼ 300 A in diameter, and mitochondria oriented perpendicular to the SMC. Neurotubules and neurofilaments are not clearly seen. These components are also virtually absent in the Mauthner cytoplasm. No ribosomes are seen in the KMnO4-fixed material. The unit membranes of the SMC of club endings show up clearly in essentially the same junctional relations described after formalin-OSO4 fixation (34). In addition, the synaptic discs in transverse section show a central beading repeating at a period of ∼ A associated with scalloping of the cytoplasmic surfaces. In oblique views, dense lines are seen repeating at a period of ∼ 90 A. In frontal views a hexagonal array of close-packed polygonal facets is seen. These repeat at a period of ∼ 95 A. Each has a central dense spot <25 A in diameter. Similar subunits are seen in the unit membranes of synaptic vesicles.

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The occurrence of a subunit pattern in the unit membranes of club endings in mauthner cell synapses in goldfish brains

Although capsids of herpes simplex virus were encountered within phagocytic vesicles, they were more commonly observed free within the cytoplasm. Stages in the release of virus from vesicles were not seen. There appeared to be five distinct steps in the process whereby the virus initiates infection: attachment, digestion of the viral envelope, digestion of the cell wall, passage of the capsid directly into the cytoplasm, and digestion of the capsid with release of the core. Antibody probably interferes with the first two stages. Images

Electron Microscopy of Herpes Simplex Virus: I. Entry

Morphology of the isolated hemagglutinin and neuraminidase subunits of influenza virus.

The ribonucleoprotein (RNP) internal components of influenza virus were separated into distinct size classes by sedimentation in glycerol gradients and examined by electron microscopy by using positive staining with uranyl acetate. The large RNP have a peak in length distribution at 90 to 110 nm, the medium, at 60 to 90 nm, and the small, at 30 to 50 nm. These lengths can be correlated with the estimated molecular weights of the ribonucleic acids contained in the various RNP size classes. The RNP structure appears to consist of a strand which is folded back on itself and coiled in a regular double-helical arrangement.

Structure of the Ribonucleoprotein of Influenza Virus

The structure and composition of the myxoviruses: II. Components released from the influenza virus particle by ether

The structure and composition of the myxoviruses. III. The interaction of influenza virus particles with cytoplasmic particles derived from normal chorioallantoic membrane cells.

L. Hoyle

Papers

The structure and composition of the myxoviruses: II. Components released from the influenza virus particle by ether

The structure and composition of the myxoviruses. III. The interaction of influenza virus particles with cytoplasmic particles derived from normal chorioallantoic membrane cells.

Amino acid composition of the protein components of influenza virus A.