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Journal of Virology, September 2001, p. 8440-8448, Vol. 75, No. 18
0022-538X/01/$04.00+0   DOI: 10.1128/JVI.75.18.8440-8448.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.

Phosphorylation of Two Serine Residues Regulates Human T-Cell Leukemia Virus Type 2 Rex Function

Murli Narayan,1,2,3 Koichi Kusuhara,4 and Patrick L. Green1,2,3,5,6,*

Departments of Veterinary Biosciences1 and Molecular Virology, Immunology, and Medical Genetics,5 Center for Retrovirus Research,2 Comprehensive Cancer Center,6 and Ohio State Biochemistry Program,3 The Ohio State University, Columbus, Ohio 43210, and Department of Pediatrics, Faculty of Medicine, Kyushu University, Higashi-ku, Fukuoka 812-8582, Japan4

Received 14 February 2001/Accepted 8 June 2001

The function of the human T-cell leukemia virus (HTLV) Rex phosphoprotein is to increase the level of the viral structural and enzymatic gene products expressed from the incompletely spliced viral RNAs containing the Rex-responsive element. The phosphorylation of HTLV type 2 Rex (Rex-2), predominantly on serine residues, correlates with an altered conformation, as detected by a gel mobility shift, and is required for specific binding to its viral RNA target sequence. Thus, the phosphorylation state of Rex in the infected cell may be a switch that determines whether the virus exists in a latent or a productive state. A mutational analysis of Rex-2 that focused on serine and threonine residues was performed to identify regions or domains within Rex-2 important for function, with a specific emphasis on identifying Rex-2 phosphorylation mutants. We identified mutations near the carboxy terminus that disrupted a novel region or domain and abrogated Rex-2 function. Mutant M17 (with S151A and S153A mutations) displayed reduced phosphorylation that correlated with reduced function. Replacement of both serine residues 151 and 153 with phosphomimetic aspartic acid restored Rex-2 function and locked Rex-2 in a phosphorylated active conformation. A mutant containing threonine residues at positions 151 and 153 displayed a phenotype indistinguishable from that of wild-type Rex. Furthermore, this same mutant showed increased threonine phosphorylation and decreased serine phosphorylation, providing conclusive evidence that one or both of these residues are phosphorylated in vivo. Our results provide the first direct evidence that the phosphorylation of Rex-2 is important for function. Further understanding of HTLV Rex phosphorylation will provide insight into the regulatory control of HTLV replication and ultimately the pathobiology of HTLV.

* Corresponding author. Mailing address: The Ohio State University, 1925 Coffey Rd., Columbus, OH 43210. Phone: (614) 688-4899. Fax: (614) 292-6473. E-mail: green.466{at}osu.edu.

Journal of Virology, September 2001, p. 8440-8448, Vol. 75, No. 18
0022-538X/01/$04.00+0   DOI: 10.1128/JVI.75.18.8440-8448.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.


This article has been cited by other articles:

  • Xie, L., Kesic, M., Yamamoto, B., Li, M., Younis, I., Lairmore, M. D., Green, P. L. (2009). Human T-Cell Leukemia Virus Type 2 Rex Carboxy Terminus Is an Inhibitory/Stability Domain That Regulates Rex Functional Activity and Viral Replication. J. Virol. 83: 5232-5243 [Abstract] [Full Text]  
  • Younis, I., Yamamoto, B., Phipps, A., Green, P. L. (2005). Human T-Cell Leukemia Virus Type 1 Expressing Nonoverlapping Tax and Rex Genes Replicates and Immortalizes Primary Human T Lymphocytes but Fails To Replicate and Persist In Vivo. J. Virol. 79: 14473-14481 [Abstract] [Full Text]  
  • Younis, I., Khair, L., Dundr, M., Lairmore, M. D., Franchini, G., Green, P. L. (2004). Repression of Human T-Cell Leukemia Virus Type 1 and Type 2 Replication by a Viral mRNA-Encoded Posttranscriptional Regulator. J. Virol. 78: 11077-11083 [Abstract] [Full Text]  
  • Narayan, M., Younis, I., D'Agostino, D. M., Green, P. L. (2003). Functional Domain Structure of Human T-Cell Leukemia Virus Type 2 Rex. J. Virol. 77: 12829-12840 [Abstract] [Full Text]  
  • Ye, J., Silverman, L., Lairmore, M. D., Green, P. L. (2003). HTLV-1 Rex is required for viral spread and persistence in vivo but is dispensable for cellular immortalization in vitro. Blood 102: 3963-3969 [Abstract] [Full Text]  


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