Surface structure of Uukuniemi virus

Abstract

Uukuniemi virus, grown in chicken embryo fibroblasts, has been studied by electron microscopy using negative staining, thin sectioning, and freezeetching techniques. The spherical virus particle measures about 95 nm in diameter. Its envelope consists of a 5-nm thick membrane covered by 8-to 10-nm long surface projections. These are composed of two polypeptide species of about the same size. Both of them can be removed by digestion with the proteolytic enzyme thermolysin except for a small fragment. The enzyme-treated particles are smooth surfaced and extremely deformable. The glycopolypeptides are clustered to form hollow cylindrical morphological units, 10 to 12 nm in diameter, with a 5-nm central cavity. Both negative staining and freeze-etching suggest that these units are penton-hexon clusters arranged in a T = 12, P = 3, icosahedral surface lattice. The membrane to which the surface subunits are attached is probably a lipid bilayer as evidenced by its double-track appearance in thin sections and the tendency of the freeze fracturing to occur within it. The strand-like nucleoprotein appears from thin-sectioning results to be to a large part located in a zone underneath the membrane.

Generation and Analysis of Infectious Virus-Like Particles of Uukuniemi Virus ( Bunyaviridae ): a Useful System for Studying Bunyaviral Packaging and Budding

“…UUK virus displayed the same morphological surface structure (Fig. 5E) as described before (52). The VLPs produced by transfection showed a particle morphology that was identical to that of the UUK virus particles (Fig.…”

“…The lipid envelope contains glycoproteins that form characteristic projections that can be visualized efficiently by electron microscopy. The projections are clustered to form hollow cylindrical units arranged in a icosahedral surface lattice (hexons and pentons) with a T12 symmetry (52). Supernatants from UUK virus-infected cells and cells transfected with only the pUUK-G N /G C plasmid or with pUUK-G N /G C together with M-CAT, pUUK-L, and pUUK-N were collected, fixed with glutaraldehyde (0.7%) to preserve the surface morphology, concentrated by ultracentrifugation, and subjected to negative staining and electron microscopy ( Fig.…”

The Glycoprotein Cytoplasmic Tail of Uukuniemi Virus ( Bunyaviridae ) Interacts with Ribonucleoproteins and Is Critical for Genome Packaging

“…We recently demonstrated that for UUK virus, the glycoproteins alone are sufficient for VLP formation, thus excluding a role for the nucleoprotein in the budding process (30), which was also confirmed in the present study. It was previously suggested that the glycoproteins are responsible for the structural stability of the virus, since spikeless particles were found to be highly deformed (44). We similarly suggest that the G N /G C proteins by themselves can generate particles and bud into the Golgi complex, and also the ER-Golgi intermediate compartment (13), when a critical glycoprotein concentration is reached.…”

Entry of Bunyaviruses into Mammalian Cells

“…Negative staining of samples containing UUKV-RED was performed with phosphotungstic acid at pH $7.4 as previously described (von Bonsdorff and Pettersson, 1975). For thin-section EM, after exposure to virus (moi $100), cells were fixed and treated as previously described (Johannsdottir et al, 2009).…”