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Journal of Virology, November 1998, p. 8620-8626, Vol. 72, No. 11
0022-538X/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.

The Herpes Simplex Virus US11 Protein Effectively Compensates for the gamma 134.5 Gene if Present before Activation of Protein Kinase R by Precluding Its Phosphorylation and That of the alpha  Subunit of Eukaryotic Translation Initiation Factor 2

Kevin A. Cassady,1 Martin Gross,2 and Bernard Roizman1,*

The Marjorie B. Kovler Viral Oncology Laboratories1 and Department of Pathology,2 The University of Chicago, Chicago, Illinois 60637

Received 29 May 1998/Accepted 24 July 1998

In herpes simplex virus-infected cells, viral gamma 134.5 protein blocks the shutoff of protein synthesis by activated protein kinase R (PKR) by directing the protein phosphatase 1alpha to dephosphorylate the alpha  subunit of eukaryotic translation initiation factor 2 (eIF-2alpha ). The amino acid sequence of the gamma 134.5 protein which interacts with the phosphatase has high homology to a domain of the eukaryotic protein GADD34. A class of compensatory mutants characterized by a deletion which results in the juxtaposition of the alpha 47 promoter next to US11, a gamma 2 (late) gene in wild-type virus-infected cells, has been described. In cells infected with these mutants, protein synthesis continues even in the absence of the gamma 134.5 gene. In these cells, PKR is activated but eIF-2alpha is not phosphorylated, and the phosphatase is not redirected to dephosphorylate eIF-2alpha . We report the following: (i) in cells infected with these mutants, US11 protein was made early in infection; (ii) US11 protein bound PKR and was phosphorylated; (iii) in in vitro assays, US11 blocked the phosphorylation of eIF-2alpha by PKR activated by poly(I-C); and (iv) US11 was more effective if present in the reaction mixture during the activation of PKR than if added after PKR had been activated by poly(I-C). We conclude the following: (i) in cells infected with the compensatory mutants, US11 made early in infection binds to PKR and precludes the phosphorylation of eIF-2alpha , whereas US11 driven by its natural promoter and expressed late in infection is ineffective; and (ii) activation of PKR by double-stranded RNA is a common impediment countered by most viruses by different mechanisms. The gamma 134.5 gene is not highly conserved among herpesviruses. A likely scenario is that acquisition by a progenitor of herpes simplex virus of a portion of the cellular GADD34 gene resulted in a more potent and reliable means of curbing the effects of activated PKR. US11 was retained as a gamma 2 gene because, like many viral proteins, it has multiple functions.

* Corresponding author. Mailing address: The Marjorie B. Kovler Viral Oncology Laboratories, The University of Chicago, 910 East 58th St., Chicago, IL 60637. Phone: (773) 702-1898. Fax: (773) 702-1631. E-mail: bernard{at}cummings.uchicago.edu.

Journal of Virology, November 1998, p. 8620-8626, Vol. 72, No. 11
0022-538X/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.


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