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Journal of Virology, September 1999, p. 7287-7296, Vol. 73, No. 9
Department of Cell Biology and Anatomy,
Cornell University Medical College, New York, New York
10021,1 and Department of Microbiology
and Molecular Genetics, Medical College of Wisconsin, Milwaukee,
Wisconsin 532262
Received 8 April 1999/Accepted 17 May 1999
Vaccinia virus encodes two protein kinases (B1 and F10) and a
dual-specificity phosphatase (VH1), suggesting that phosphorylation and
dephosphorylation of substrates on serine/threonine and tyrosine residues are important in regulating diverse aspects of the viral life
cycle. Using a recombinant in which expression of the H1 phosphatase
can be regulated experimentally (vindH1), we have previously demonstrated that repression of H1 leads to the maturation of noninfectious virions that contain several hyperphosphorylated substrates (K. Liu et al., J. Virol. 69:7823-7834). In this
report, we demonstrate that among these is a 25-kDa protein that is
phosphorylated on tyrosine residues in H1-deficient virions and can be
dephosphorylated by recombinant H1. We demonstrate that the 25-kDa
phosphoprotein represents the product of the A17 gene and that A17 is
phosphorylated on serine, threonine, and tyrosine residues during
infection. Detection of phosphotyrosine within A17 is abrogated when
Tyr203 (but not Tyr3, Tyr6, or
Tyr7) is mutated to phenylalanine, suggesting strongly that
this amino acid is the site of tyrosine phosphorylation.
Phosphorylation of A17 fails to occur during nonpermissive infections
performed with temperature-sensitive mutants defective in the F10
kinase. Our data suggest that this enzyme, which was initially
characterized as a serine/threonine kinase, might in fact have dual
specificity. This hypothesis is strengthened by the observation that
Escherichia coli induced to express F10 contain multiple
proteins which are recognized by antiphosphotyrosine antiserum. This
study presents the first evidence for phosphotyrosine signaling during
vaccinia virus infection and implicates the F10 kinase and the H1
phosphatase as the dual-specificity enzymes that direct this cycle of
reversible phosphorylation.
0022-538X/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.
Tyrosine Phosphorylation of A17 during Vaccinia Virus Infection:
Involvement of the H1 Phosphatase and the F10 Kinase

*
Corresponding author. Mailing address: Department of
Microbiology and Molecular Genetics, Medical College of Wisconsin, 8701 Watertown Plank Rd., Milwaukee, WI 53226. Phone: (414) 456-8253. Fax:
(414) 456-6535. E-mail: ptrakt{at}mcw.edu.
Present address: Laboratoire de Biologie des Retrovirus,
Departement de Virologie, Institut Pasteur, 75724 Paris Cedex 15, France.
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