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Journal of Virology, March 1999, p. 2193-2200, Vol. 73, No. 3
0022-538X/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.

Intracellular Redistribution of Truncated La Protein Produced by Poliovirus 3Cpro-Mediated Cleavage

Kazuko Shiroki,1,* Takeshi Isoyama,1 Shusuke Kuge,1 Toshihiko Ishii,1 Shinobu Ohmi,2 Syoji Hata,3 Koichi Suzuki,3 Yoshinari Takasaki,4 and Akio Nomoto1

Department of Microbiology1 and Department of Bacterial Infection,2 Institute of Medical Science, University of Tokyo, 4-6-1 Shirokanedai, Minato-ku, Tokyo 108-8639, Institute of Molecular and Cellular Biosciences, University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo 113-0032,3 and Division of Rheumatology, Department of Medicine, Juntendo University School of Medicine, 3-1-3 Hongo, Bunkyo-ku, Tokyo 113-8421,4 Japan

Received 29 June 1998/Accepted 16 November 1998

The La autoantigen (also known as SS-B), a cellular RNA binding protein, may shuttle between the nucleus and cytoplasm, but it is mainly located in the nucleus. La protein is redistributed to the cytoplasm after poliovirus infection. An in vitro translation study demonstrated that La protein stimulated the internal initiation of poliovirus translation. In the present study, a part of the La protein was shown to be cleaved in poliovirus-infected HeLa cells, and this cleavage appeared to be mediated by poliovirus-specific protease 3C (3Cpro). Truncated La protein (dl-La) was produced in vitro from recombinant La protein by cleavage with purified 3Cpro at only one Gln358-Gly359 peptide bond in the 408-amino-acid (aa) sequence of La protein. The dl-La expressed in L cells was detected in the cytoplasm. However, green fluorescence protein linked to the C-terminal 50-aa sequence of La protein was localized in the nucleus, suggesting that this C-terminal region contributes to the steady-state nuclear localization of the intact La protein in uninfected cells. The dl-La retained the enhancing activity of translation initiation driven by poliovirus RNA in rabbit reticulocyte lysates. These results suggest that La protein is cleaved by 3Cpro in the course of poliovirus infection and that the dl-La is redistributed to the cytoplasm. dl-La, as well as La protein, may play a role in stimulating the internal initiation of poliovirus translation in the cytoplasm.

* Corresponding author. Mailing address: Department of Microbiology, Institute of Medical Science, The University of Tokyo, 4-6-1 Shirokanedai, Minato-ku, Tokyo 108-8639, Japan. Phone: 81-3-5449-5503. Fax: 81-3-5449-5408. E-mail: kshiroki{at}ims.u-tokyo.ac.jp.

Journal of Virology, March 1999, p. 2193-2200, Vol. 73, No. 3
0022-538X/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.


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