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Journal of Virology, August 2000, p. 7508-7517, Vol. 74, No. 16
Laboratory of Viral Diseases, National
Institute of Allergy and Infectious Diseases, National Institutes
of Health, Bethesda, Maryland 20892-0445
Received 22 March 2000/Accepted 18 May 2000
The vaccinia virus H3L open reading frame encodes a 324-amino-acid
immunodominant membrane component of virus particles. Biochemical and
microscopic studies demonstrated that the H3L protein was expressed
late in infection, accumulated in the cytoplasmic viral factory
regions, and associated primarily with amorphous material near immature
virions and with intracellular virion membranes. Localization of the
H3L protein on the surfaces of viral particles and anchorage via the
hydrophobic tail were consistent with its extraction by NP-40 in the
absence of reducing agents, its trypsin sensitivity, its reactivity
with a membrane-impermeable biotinylation reagent, and its immunogold
labeling with an antibody to a peptide comprising amino acids 247 to
259. The H3L protein, synthesized in a coupled in vitro
transcription/translation system, was tightly anchored to membranes as
determined by resistance to Na2CO3 (pH 11)
extraction and cytoplasmically oriented as shown by sensitivity to
proteinase K digestion. Further studies demonstrated that membrane insertion of the H3L protein occurred posttranslationally and that the
C-terminal hydrophobic domain was necessary and sufficient for this to
occur. These data indicated that the H3L protein is a member of the
C-terminal anchor family and supported a model in which it is
synthesized on free ribosomes and inserts into the membranes of viral
particles during their maturation.
0022-538X/00/$04.00+0
Characterization of the Vaccinia Virus H3L Envelope
Protein: Topology and Posttranslational Membrane Insertion via the
C-Terminal Hydrophobic Tail

*
Corresponding author. Mailing address: 4 Center Dr.,
MSC 0445, NIH, Bethesda, MD 20892-0455. Phone: (301) 496-9869. Fax:
(301) 480-1147. E-mail: bmoss{at}nih.gov.
Present address: Laboratório de Vírus, Departamento
de Microbiologia, Instituto de Ciências Biológicas da
Universidade Federal de Minas Gerais, Belo Horizonte, MG, Brazil.
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