Uukuniemi Virus

Jantti J; Hilden P; Ronka H; Makiranta V; Keranen S; Kuismanen E.
      Immunocytochemical analysis of Uukuniemi virus budding compartments:    role of the intermediate compartment and the Golgi stack in virus maturation.
    Journal of Virology, 1997 Feb, 71(2):1162-72.
        (UI:  97151102)

Abstract: Previous studies have suggested that Uukuniemi virus, a bunyavirus,
matures at the membranes of the Golgi complex. In this study we have
employed immunocytochemical techniques to analyze in detail the budding
compartment(s) of the virus. Electron microscopy of infected BHK-21 cells
showed that virus particles are found in the cisternae throughout the Golgi
stack. Within the cisternae, the virus particles were located
preferentially in the dilated rims. This would suggest that virus budding
may begin at or before the cis Golgi membranes. The virus budding
compartment was studied further by immunoelectron microscopy with a
pre-Golgi intermediate compartment marker, p58, and a Golgi stack
marker  protein, mannosidase II (ManII). Virus particles and budding
virus were detected in ManII-positive Golgi stack membranes and, interestingly,
in both juxtanuclear and peripheral p58-positive elements of the intermediate compartment.
In cells incubated at 15 degrees C the nucleocapsid and virus envelope proteins were
seen to accumulate in the intermediate compartment.

Immunoelectron microscopy demonstrated that at 15 degrees C the nucleocapsid
is associated with membranes that show a characteristic distribution and
tubulo-vesicular morphology of the pre-Golgi intermediate
compartment. These membranes contained virus particles in the lumen. The
results indicate that the first site of formation of Uukuniemi virus particles is the
pre-Golgi intermediate compartment and that virus budding
continues in the Golgi stack. The results raise questions about the
intracellular transport pathway of the virus particles, which are 100 to
120 nm in diameter and are therefore too large to be transported in the
60-nm-diameter vesicles postulated to function in the intra-Golgi
transport. The distribution of the virus in the Golgi stack may imply that
the cisternae themselves have a role in the vectorial transport of virus
particles.

La Crosse Virus

Pekosz A; Gonzalez-Scarano F.
      The extracellular domain of La Crosse virus G1 forms oligomers and
      undergoes pH-dependent conformational changes.
    Virology, 1996 Nov 1, 225(1):243-7.
        (UI:  97076238)

Abstract: The La Crosse virus G1 glycoprotein plays a critical role in virus
    binding to susceptible cells and in the subsequent fusion of viral and
    cellular membranes. A soluble form of the G1 glycoprotein (sG1) prepared in
    a recombinant baculovirus system mimics the cell-binding pattern of La
    Crosse virus and inhibits La Crosse virus infection (A. Pekosz et al.,
    Virology 214, 339-348, 1995), presumably by competing for a cellular
    receptor, a finding that implies that sG1 can perform some functions absent
    G2, the smaller of the two bunyavirus glycoproteins. We have performed
    experiments to determine whether sG1 is present as an oligomer and whether
    it undergoes the conformational changes associated with fusion
    (F. Gonzalez-Scarano, Virology 140, 209-216, 1985). Our results indicate that
    both sG1 and native G1 undergo similar changes in conformation after
    exposure to an acidic environment, as detected by reactivity with
    monoclonal antibodies. Furthermore, using chemical cross-linking, both
    proteins were detected as oligomers (most likely dimers). Sucrose density
    gradient analysis of sG1 verified that it was present in monomeric and
    oligomeric forms. These results demonstrate that the isolated G1
    glycoprotein can undergo a pH-dependent change in conformation in the
    absence of its transmembrane and cytoplasmic tall domains and that the
    extracellular portion of the glycoprotein can oligomerize.