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Journal of Virology, December 2001, p. 12153-12160, Vol. 75, No. 24
0022-538X/01/$04.00+0   DOI: 10.1128/JVI.75.24.12153-12160.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.

Functional Specialization and Evolution of Leader Proteinases in the Family Closteroviridae

Chih-Wen Peng,1 Valera V. Peremyslov,1 Arcady R. Mushegian,2 William O. Dawson,3 and Valerian V. Dolja1,*

Department of Botany and Plant Pathology and Center for Gene Research and Biotechnology, Oregon State University, Corvallis, Oregon 973311; Akkadix Corporation, La Jolla, California 920372; and Department of Plant Pathology, University of Florida, Lake Alfred, Florida 338503

Received 23 April 2001/Accepted 18 September 2001

Members of the Closteroviridae and Potyviridae families of the plant positive-strand RNA viruses encode one or two papain-like leader proteinases. In addition to a C-terminal proteolytic domain, each of these proteinases possesses a nonproteolytic N-terminal domain. We compared functions of the several leader proteinases using a gene swapping approach. The leader proteinase (L-Pro) of Beet yellows virus (BYV; a closterovirus) was replaced with L1 or L2 proteinases of Citrus tristeza virus (CTV; another closterovirus), P-Pro proteinase of Lettuce infectious yellows virus (LIYV; a crinivirus), and HC-Pro proteinase of Tobacco etch virus (a potyvirus). Each foreign proteinase efficiently processed the chimeric BYV polyprotein in vitro. However, only L1 and P-Pro, not L2 and HC-Pro, were able to rescue the amplification of the chimeric BYV variants. The combined expression of L1 and L2 resulted in an increased RNA accumulation compared to that of the parental BYV. Remarkably, this L1-L2 chimera exhibited reduced invasiveness and inability to move from cell to cell. Similar analyses of the BYV hybrids, in which only the papain-like domain of L-Pro was replaced with those derived from L1, L2, P-Pro, and HC-Pro, also revealed functional specialization of these domains. In subcellular-localization experiments, distinct patterns were observed for the leader proteinases of BYV, CTV, and LIYV. Taken together, these results demonstrated that, in addition to a common proteolytic activity, the leader proteinases of closteroviruses possess specialized functions in virus RNA amplification, virus invasion, and cell-to-cell movement. The phylogenetic analysis suggested that functionally distinct L1 and L2 of CTV originated by a gene duplication event.

* Corresponding author. Mailing address: Department of Botany and Plant Pathology, Oregon State University, Cordley Hall 2082, Corvallis, OR 97331. Phone: (541) 737-5472. Fax: (541) 737-3573. E-mail: doljav{at}bcc.orst.edu.

Journal of Virology, December 2001, p. 12153-12160, Vol. 75, No. 24
0022-538X/01/$04.00+0   DOI: 10.1128/JVI.75.24.12153-12160.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.


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Copyright © 2001 by the American Society for Microbiology. All rights reserved.