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J Virol, August 1998, p. 6398-6405, Vol. 72, No. 8
0022-538X/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.
Analysis of Rotavirus Nonstructural Protein NSP5
Phosphorylation
J.
Blackhall,
M.
Muñoz,
A.
Fuentes, and
G.
Magnusson*
Department of Medical Biochemistry and
Microbiology, Biomedical Centre, Uppsala University, Uppsala,
Sweden
Received 10 November 1997/Accepted 17 April 1998
The rotavirus nonstructural phosphoprotein NSP5 is encoded by a
gene in RNA segment 11. Immunofluorescence analysis of fixed cells
showed that NSP5 polypeptides remained confined to viroplasms even at a late stage when provirions migrated from these structures. When NSP5 was expressed in COS-7 cells in the absence of other viral
proteins, it was uniformly distributed in the cytoplasm. Under these
conditions, the 26-kDa polypeptide predominated. In the presence of the protein phosphatase inhibitor okadaic acid, the
highly phosphorylated 28- and 32- to 35-kDa polypeptides
were formed. Also, the fully phosphorylated protein had a
homogeneous cytoplasmic distribution in transfected
cells. In rotavirus SA11-infected cells, NSP5 synthesis was
detectable at 2 h postinfection. However, the newly
formed 26-kDa NSP5 was not converted to the 28- to 35-kDa forms until
approximately 2 h later. Also, the protein kinase activity of
isolated NSP5 was not detectable until the 28- and 30- to 35-kDa
NSP5 forms had been formed. NSP5 immunoprecipitated from extracts of
transfected COS-7 cells was active in autophosphorylation in vitro,
demonstrating that other viral proteins were not required for this
function. Treatment of NSP5-expressing cells with staurosporine, a
broad-range protein kinase inhibitor, had only a limited negative effect on the phosphorylation of the viral polypeptide.
Staurosporine did not inhibit autophosphorylation of NSP5 in
vitro. Together, the data support the idea that NSP5 has an
autophosphorylation activity that is positively regulated by
addition of phosphate residues at some positions.
*
Corresponding author. Mailing address: Department of
Medical Biochemistry and Microbiology, Box 582, S-751 23 Uppsala,
Sweden. Phone: 46-18-4714560. Fax: 46-18-509876. E-mail:
Goran.Magnusson{at}imim.uu.se.

Present address: Instituto de Biotecnología, CICV-INTA
Castelar, CC77, 1708 Moron, Buenos Aires, Argentina.
J Virol, August 1998, p. 6398-6405, Vol. 72, No. 8
0022-538X/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.
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