On the structure of filamentous forms of influenza virus
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Conclusions and Summary
The observation of two filamentous strains of influenza A viruses shows that filaments present a surface structure identical to that of spheres, as already observed byChoppin et al. (3). This outer shell is comprised of dumb-bell shaped subunits (80 Å from axis to axis). The diameter of each small grain of the dumb-bell is about 30 A and they are about 25 Å apart. As is clearly seen in the sections, these subunits are supported by a continuous membrane, as already suggested byMorgan et al. (1) and byHoyle et al. (8).
In the cross section of the filaments, an internal material is also revealed; this seems to be unevenly distributed along the filament and appears to be constituted of ordered little grains, 50 Å in diameter. This material is dissimilar to that observed in the spheres, in which it has the appearance of very thin threads, about 25 Å thick. The frequent presence of septa (in about 25% of filaments) can be clearly seen. Sometimes, instead of septa, a regular succession of constrictions is observed, which is in keeping with the hypothesis that some of the spheres are formed from the filaments by a process of segmentation.
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