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Journal of Virology, August 2000, p. 7518-7528, 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 17 May 2000
The C-terminal membrane anchor protein encoded by the H3L open
reading frame of vaccinia virus is located on the surfaces of
intracellular mature virions. To investigate the role of the H3L
protein, we constructed deletion (vH3
0022-538X/00/$04.00+0
Effects of Deletion or Stringent Repression of the
H3L Envelope Gene on Vaccinia Virus Replication

) and inducible (vH3i) null
mutants. The H3L protein was not detected in lysates of cells infected
with vH3
or vH3i in the absence of inducer. Under these conditions,
plaques were small and round instead of large and comet shaped,
indicative of decreased virus replication or cell-to-cell spread. The
mutant phenotype was correlated with reduced yields of infectious
intra- and extracellular virus in one-step growth experiments. The
defect in vH3i replication could not be attributed to a role of the H3L
protein in virus binding, internalization, or any event prior to late
gene expression. Electron microscopic examination of cells infected
with vH3
or vH3i in the absence of inducer revealed that virion
assembly was impaired, resulting in a high ratio of immature to mature
virus forms with an accumulation of crescent membranes adjacent to
granular material and DNA crystalloids. The absence of the H3L protein
did not impair the membrane localization of virion surface proteins
encoded by the A27L, D8L, and L1R genes. The wrapping of virions and
actin tail formation were not specifically blocked, but there was an
apparent defect in low-pH-mediated syncytium formation that could be
attributed to decreased virus particle production. The phenotypes of
the H3L deletion and repression mutants were identical to each other
but differed from those produced by null mutations of genes encoding
other vaccinia virus membrane components.
*
Corresponding author. Mailing address: 4 Center Dr.,
MSC 0445, National Institutes of Health, 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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