One of the key mediators of the antiviral and antiproliferative actions of interferon is double-stranded-RNA-dependent protein kinase (PKR). PKR activity is also involved in the regulation of cell proliferation, apoptosis and signal transduction. We have recently identified PACT, a novel protein activator of PKR, as an important modulator of PKR activity in cells in the absence of viral infection. PACT heterodimerizes with PKR and activates it by direct protein—protein interactions. Endogenous PACT acts as an activator of PKR in response to diverse stress signals, such as serum starvation and peroxide or arsenite treatment, and is therefore a novel, stress-modulated physiological activator of PKR. In this study, we have characterized the functional domains of PACT that are required for PKR activation. Our results have shown that, unlike the N-terminal conserved domains 1 and 2, the third conserved domain of PACT is dispensable for its binding of double-stranded RNA and inter action with PKR. However, a deletion of domain 3 results in a loss of PKR activation ability, in spite of a normal interaction with PKR, thereby indicating that domain 3 plays an essential role in PKR activation. Purified recombinant domain 3 could also activate PKR efficiently in vitro. Our results indicate that, although dispensable for PACT's high-affinity interaction with PKR, the third motif is essential for PKR activation. In addition, domain 3 and eukaryotic initiation factor 2α both interact with PKR through the same region within PKR, which we have mapped to lie between amino acid residues 318 and 551.
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August 2002
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Research Article|
August 15 2002
The C-terminal, third conserved motif of the protein activator PACT plays an essential role in the activation of double-stranded-RNA-dependent protein kinase (PKR)
Xu HUANG;
Xu HUANG
Department of Biological Sciences, University of South Carolina, 700 Sumter Street, Columbia, SC 29208, U.S.A.
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Brian HUTCHINS;
Brian HUTCHINS
Department of Biological Sciences, University of South Carolina, 700 Sumter Street, Columbia, SC 29208, U.S.A.
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Rekha C. PATEL
Rekha C. PATEL
1
Department of Biological Sciences, University of South Carolina, 700 Sumter Street, Columbia, SC 29208, U.S.A.
1To whom correspondence should be addressed (e-mail patelr@sc.edu).
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Publisher: Portland Press Ltd
Received:
January 31 2002
Revision Received:
April 16 2002
Accepted:
May 02 2002
Online ISSN: 1470-8728
Print ISSN: 0264-6021
The Biochemical Society, London ©2002
2002
Biochem J (2002) 366 (1): 175–186.
Article history
Received:
January 31 2002
Revision Received:
April 16 2002
Accepted:
May 02 2002
Citation
Xu HUANG, Brian HUTCHINS, Rekha C. PATEL; The C-terminal, third conserved motif of the protein activator PACT plays an essential role in the activation of double-stranded-RNA-dependent protein kinase (PKR). Biochem J 15 August 2002; 366 (1): 175–186. doi: https://doi.org/10.1042/bj20020204
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