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Journal of Virology, June 2006, p. 6165-6170, Vol. 80, No. 12
0022-538X/06/$08.00+0 doi:10.1128/JVI.02331-05
Copyright © 2006, American Society for Microbiology. All Rights Reserved.
Howard Hughes Medical Institute, G.W. Hooper Foundation, Departments of Microbiology and Immunology and Medicine, University of California, San Francisco, California 94143
Received 5 November 2005/ Accepted 28 March 2006
Kaposi's sarcoma-associated herpesvirus encodes a protein, kaposin B, which is composed of multiple copies of 23-amino-acid direct repeats, termed DR2 and DR1. Kaposin B enhances the release of pathogenetically important proinflammatory cytokines by activating the p38 mitogen-activated protein kinase (MAPK)-MK2 kinase pathway and blocking cytokine mRNA decay. Here, we show that this mRNA stabilization function requires both the DR2 and DR1 elements of kaposin B; a monomeric form of the protein consisting of one copy of each repeat retains function. Furthermore, we show that p38 MAPK is capable of directly phosphorylating kaposin B in vitro and map the site of phosphorylation to a specific serine residue in DR1. Mutational ablation of this serine abolishes phosphorylation of the protein by p38 MAPK but does not affect kaposin B's ability to extend mRNA half-life.
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