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Journal of Virology, December 2003, p. 13106-13116, Vol. 77, No. 24
0022-538X/03/$08.00+0 DOI: 10.1128/JVI.77.24.13106-13116.2003
Copyright © 2003, American
Society for
Microbiology. All Rights Reserved.
Functional Analysis of nsP3 Phosphoprotein Mutants of Sindbis Virus
Indra Dé,
Cori Fata-Hartley,
Stanley G. Sawicki, and Dorothea L. Sawicki*
Department
of Microbiology, Medical College of Ohio, Toledo, Ohio
43699
Received 17 June 2003/
Accepted 15 September 2003
Alphavirus
nsP3 phosphoprotein is essential for virus replication and functions
initially within polyprotein P123 or P23 components of the short-lived
minus-strand replicase, and upon polyprotein cleavage, mature nsP3
likely functions also in plus-strand synthesis. We report the
identification of a second nsP3 mutant from among the A complementation
group of Sindbis virus (SIN) heat-resistant strain, ts
RNA-negative mutants. The ts138 mutant possessed a change of
G4303 to C, predicting an Ala68-to-Gly alteration that altered a
conserved His-Ala-Val tripeptide in the ancient (pre-eukaryotic),
"X" or histone 2A phosphoesterase-like macrodomain that
in SIN encompasses nsP3 residues 1 to 161 and whose role is unknown. We
undertook comparative analysis of three nsP3 N-terminal
region mutants and observed (i) that nsP3 and nsP2
functioned initially as a single unit as deduced from complementation
analysis and in agreement with our previous studies, (ii) that the
degree of phosphorylation varied among the nsP3 mutants, and (iii) that
reduced phosphorylation of nsP3 correlated with reduced minus-strand
synthesis. The most striking phenotype was exhibited by ts4
(Ala268 to Val), which after shift to 40°C made significantly
underphosphorylated P23/nsP3 and lost selectively the ability to make
minus strands. After shift to 40°C, mutant ts7 (Phe312
to Ser) made phosphorylated P23/nsP3 and minus strands but failed to
increase plus-strand synthesis. Macrodomain mutant ts138 was
intermediate, making at 40°C partially phosphorylated P23/nsP3
and reduced amounts of minus strands. The mutants were able to assemble
their nsPs at 40°C into complexes that were membrane
associated. Our analyses argue that P23/P123 phosphorylation is
affected by macrodomain and Ala268 region sequences and in turn affects
the efficient transcription of the alphavirus
genome.
* Corresponding
author. Mailing address: Department of Microbiology, Medical College of
Ohio, Toledo, OH 43699. Phone: (419) 383-4337. Fax: (419) 383-3002.
E-mail:
dsawicki{at}mco.edu.
Present
address: Infectious Diseases, Department of Medicine, M. D.
Anderson, University of Texas, Houston, Tex.
Present
address: Department of Biochemistry, Institute of Molecular Virology,
University of WisconsinMadison, Madison,
Wis.
Journal of Virology, December 2003, p. 13106-13116, Vol. 77, No. 24
0022-538X/03/$08.00+0 DOI: 10.1128/JVI.77.24.13106-13116.2003
Copyright © 2003, American
Society for
Microbiology. All Rights Reserved.
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