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J. Virol., 07 1995, 4103-4111, Vol 69, No. 7
TG Senkevich, EJ Wolffe and RM Buller
We have previously described a gene of ectromelia virus (EV) that codes for
a 28-kDa RING zinc finger-containing protein (p28) that is nonessential for
virus growth in cell culture but is critical for EV pathogenicity in mice
(T. G. Senkevich, E. V. Koonin, and R. M. L. Buller, Virology 198:118-128;
1994). Here, we show that, unlike all tested cell cultures, the expression
of p28 is required for in vitro replication of EV in murine resident
peritoneal macrophages. In macrophages infected with the p28- mutant, viral
DNA replication was not detected, whereas the synthesis of at least two
early proteins was observed. Immunofluorescence and biochemical analyses
showed that in EV- infected macrophages or BSC-1 cells, p28 is associated
with virus factories. By use of a vaccinia virus expression system to
examine different truncated versions of p28, it was shown that the
disruption of the specific structure of the RING domain had no influence on
the intracellular localization of this protein. When viral DNA replication
was inhibited with cytosine arabinoside, p28 was found in distinct, focal
structures that may be precursors to the factories. We hypothesize that in
macrophages, which are highly specialized, nondividing cells, p28
substitutes for an unknown cellular factor(s) that may be required for
viral DNA replication or a stage of virus reproduction between the
expression of early genes and the onset of DNA synthesis. In the absence of
p28, the attenuation of EV pathogenicity can be explained by a failure of
the virus to replicate in macrophage lineage cells at all successive steps
in the spread of virus from the skin to its target organ, the liver.
Copyright © 1995, American Society for Microbiology
Ectromelia virus RING finger protein is localized in virus factories and is required for virus replication in macrophages
Laboratory of Viral Diseases, National Institute of Allergy and Infectious Diseases, Bethesda, Maryland 20892, USA.
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