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Journal of Virology, June 2006, p. 5807-5821, Vol. 80, No. 12
0022-538X/06/$08.00+0 doi:10.1128/JVI.00254-06
Copyright © 2006, American Society for Microbiology. All Rights Reserved.
Monika Fasler,3,
Vitaly Boyko,2,
and
Manfred Heinlein1,2,3*
Institut Biologie Moléculaire des Plantes, 12, rue du Général Zimmer, 67084 Strasbourg Cedex, France,1 Friedrich Miescher Institute for Biomedical Research, P.O. Box 2543, CH-4002 Basel, Switzerland,2 Plant Health Unit, Botanisches Institut, Hebelstrasse 1, CH-4056 Basel, Switzerland3
Received 3 February 2006/ Accepted 18 March 2006
The movement protein (MP) of Tobacco mosaic virus mediates the cell-to-cell transport of viral RNA through plasmodesmata, cytoplasmic cell wall channels for direct cell-to-cell communication between adjacent cells. Previous in vivo studies demonstrated that the RNA transport function of the protein correlates with its association with microtubules, although the exact role of microtubules in the movement process remains unknown. Since the binding of MP to microtubules is conserved in transfected mammalian cells, we took advantage of available mammalian cell biology reagents and tools to further address the interaction in flat-growing and transparent COS-7 cells. We demonstrate that neither actin, nor endoplasmic reticulum (ER), nor dynein motor complexes are involved in the apparent alignment of MP with microtubules. Together with results of in vitro coprecipitation experiments, these findings indicate that MP binds microtubules directly. Unlike microtubules associated with neuronal MAP2c, MP-associated microtubules are resistant to disruption by microtubule-disrupting agents or cold, suggesting that MP is a specialized microtubule binding protein that forms unusually stable complexes with microtubules. MP-associated microtubules accumulate ER membranes, which is consistent with a proposed role for MP in the recruitment of membranes in infected plant cells and may suggest that microtubules are involved in this process. The ability of MP to interfere with centrosomal
-tubulin is independent of microtubule association with MP, does not involve the removal of other tested centrosomal markers, and correlates with inhibition of centrosomal microtubule nucleation activity. These observations suggest that the function of MP in viral movement may involve interaction with the microtubule-nucleating machinery.
Present address: Department of Disease and Stress Biology, John Innes Center, Norwich NR47UH, United Kingdom.
Present address: Friedrich Miescher Institute for Biomedical Research, CH-4002 Basel, Switzerland.
Present address: HIV Drug Resistance Program, NCI-Frederick, Frederick, MD 21702-1201.
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