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Journal of Virology, January 2005, p. 732-744, Vol. 79, No. 2
0022-538X/05/$08.00+0 doi:10.1128/JVI.79.2.732-744.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.
Involvement of Influenza Virus PA Subunit in Assembly of Functional RNA Polymerase Complexes
Atsushi Kawaguchi,
Tadasuke Naito, and
Kyosuke Nagata*
Department of Infection Biology, Graduate School of Comprehensive Human Sciences and Institute of Basic Medical Sciences, University of Tsukuba, Tsukuba, Japan
Received 12 June 2004/
Accepted 3 September 2004
The RNA-dependent RNA polymerase of influenza virus consists of three subunits, PB1, PB2, and PA, and synthesizes three kinds of viral RNAs, vRNA, cRNA, and mRNA. PB1 is a catalytic subunit; PB2 recognizes the cap structure for generation of the primer for transcription; and PA is thought to be involved in viral RNA replication. However, the process of polymerase complex assembly and the exact nature of polymerase complexes involved in synthesis of the three different RNA species are not yet clear. ts53 virus is a temperature-sensitive (ts) mutant derived from A/WSN/33 (A. Sugiura, M. Ueda, K. Tobita, and C. Enomoto, Virology 65:363-373, 1975). We confirmed that the mRNA synthesis level of ts53 remains unaffected at the nonpermissive temperature, whereas vRNA synthesis is largely reduced. Sequencing of the gene encoding ts53 PA and recombinant virus rescue experiments revealed that an amino acid change from Leu to Pro at amino acid position 226 is causative of temperature sensitivity. By glycerol density gradient analyses of nuclear extracts prepared from wild-type virus-infected cells, we found that polymerase proteins sediment in three fractions: one (H fraction) consists of RNP complexes, another (M fraction) contains active polymerases but not viral RNA, and the other (L fraction) contains inactive forms of polymerases. Pulse-chase experiments showed that polymerases in the L fraction are converted to those in the M fraction. In ts53-infected cells, polymerases accumulated in the L fraction. These results strongly suggest that PA is involved in the assembly of functional viral RNA polymerase complexes from their inactive intermediates.
* Corresponding author. Mailing address: Department of Infection Biology, Institute of Basic Medical Sciences, University of Tsukuba, 1-1-1 Tennodai, Tsukuba 305-8575, Japan. Phone: 81-298-53-3233. Fax: 81-298-53-3233. E-mail:
knagata{at}md.tsukuba.ac.jp.
Journal of Virology, January 2005, p. 732-744, Vol. 79, No. 2
0022-538X/05/$08.00+0 doi:10.1128/JVI.79.2.732-744.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.
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