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Journal of Virology, March 2003, p. 2843-2849, Vol. 77, No. 5
0022-538X/03/$08.00+0 DOI: 10.1128/JVI.77.5.2843-2849.2003
Copyright © 2003, American Society for Microbiology. All Rights Reserved.
Department of Botany and Plant Pathology and Center for Gene Research and Biotechnology, Oregon State University, Corvallis, Oregon 97331
Received 4 September 2002/ Accepted 22 November 2002
The 66-kDa leader proteinase (L-Pro) of the Beet yellows virus (BYV) possesses a nonconserved N-terminal domain and a conserved, papain-like C-terminal domain. Previous work revealed that the N-terminal domain functions in RNA amplification, whereas the C-terminal domain is required for autoproteolysis. Alanine-scanning mutagenesis was applied to complete the functional analysis of L-Pro throughout the virus life cycle. This analysis indicated that the C-terminal domain of L-Pro, in addition to being required for proteolysis, also functions in RNA amplification and that these two functions are genetically separable. Examination of the role of L-Pro in BYV cell-to-cell movement revealed that none of the 20 examined replication-competent mutants was movement defective. In contrast, six of the L-Pro mutations affected the long-distance transport of BYV to various degrees, whereas three mutations completely abolished the transport. Because these mutations were located throughout the protein molecule, both domains of L-Pro function in virus transport. We conclude that in addition to previously identified functions of L-Pro, it also serves as the BYV long-distance transport factor.
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