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Journal of Virology, October 2000, p. 9175-9183, Vol. 74, No. 19
Laboratory of Viral Diseases, National
Institute of Allergy and Infectious Diseases, National Institutes
of Health, Bethesda, Maryland 20892-0445
Received 12 June 2000/Accepted 13 July 2000
Vaccinia virus encodes two glutaredoxins, O2L and G4L, both of
which exhibit thioltransferase and dehydroascorbate reductase activities in vitro. Although O2L was previously found to be
dispensable for virus replication, we now show that G4L is necessary
for virion morphogenesis. RNase protection and Western blotting assays
indicated that G4L was expressed at late times after infection and was
incorporated into mature virus particles. Attempts to isolate a mutant
virus with a deleted G4L gene were unsuccessful, suggesting that the protein was required for virus replication. This interpretation was
confirmed by the construction and characterization of a conditional lethal recombinant virus with an inducible copy of the G4L gene replacing the original one. Expression of G4L was proportional to the
concentration of inducer, and the amount of glutaredoxin could be
varied from barely detectable to greater than normal amounts of
protein. Immunogold labeling revealed that the induced G4L protein was
associated with immature and mature virions and adjacent cytoplasmic
depots. In the absence of inducer, the production of infectious virus
was severely inhibited, though viral late protein synthesis appeared
unaffected except for decreased maturation-dependent proteolytic
processing of certain core components. Electron microscopy of cells
infected under nonpermissive conditions revealed an accumulation of
crescent membranes on the periphery of electron-dense globular masses
but few mature particles. We concluded that the two glutaredoxin homologs encoded by vaccinia virus have different functions and that
G4L has a role in virion morphogenesis, perhaps by acting as a redox protein.
0022-538X/00/$04.00+0
A Glutaredoxin, Encoded by the G4L Gene of Vaccinia
Virus, Is Essential for Virion Morphogenesis
*
Corresponding author. Mailing address: Laboratory of
Viral Diseases, National Institutes of Health, 4 Center Dr., MSC 0445, Bethesda, MD 20892-0455. Phone: (301) 496-9869. Fax: (301) 480-1147. E-mail: bmoss{at}nih.gov.
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