Affiliation:
1. Department of Botany and Plant Pathology and Center for Gene Research and Biotechnology, Oregon State University, Corvallis, Oregon 973311;
2. Akkadix Corporation, La Jolla, California 920372; and
3. Department of Plant Pathology, University of Florida, Lake Alfred, Florida 338503
Abstract
ABSTRACT
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.
Publisher
American Society for Microbiology
Subject
Virology,Insect Science,Immunology,Microbiology
Cited by
71 articles.
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