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Journal of Virology, September 1998, p. 7160-7169, Vol. 72, No. 9
Department of Biology, Indiana University,
Bloomington, Indiana 47405,1 and
Department of Plant Pathology and Agricultural Research
Service, U.S. Department of Agriculture, University of Nebraska,
Lincoln, Nebraska 685832
Received 13 April 1998/Accepted 11 June 1998
Brome mosaic virus (BMV), a positive-strand RNA virus, encodes two
replication proteins: the 2a protein, which contains polymerase-like sequences, and the 1a protein, with N-terminal putative capping and
C-terminal helicase-like sequences. These two proteins are part of a
multisubunit complex which is necessary for viral RNA replication. We
have previously shown that the yeast two-hybrid assay consistently
duplicated results obtained from in vivo RNA replication assays and
biochemical assays of protein-protein interaction, thus permitting the
identification of additional interacting domains. We now map an
interaction found to take place between two 1a proteins. Using
previously characterized 1a mutants, a perfect correlation was found
between the in vivo phenotypes of these mutants and their abilities to
interact with wild-type 1a (wt1a) and each other. Western blot analysis
revealed that the stabilities of many of the noninteracting mutant
proteins were similar to that of wt1a. Deletion analysis of 1a revealed
that the N-terminal 515 residues of the 1a protein are required and
sufficient for 1a-1a interaction. This intermolecular interaction
between the putative capping domain and itself was detected in another
tripartite RNA virus, cucumber mosaic virus (CMV), suggesting that the
1a-1a interaction is a feature necessary for the replication of
tripartite RNA viruses. The boundaries for various activities are
placed in the context of the predicted secondary structures of several 1a-like proteins of members of the alphavirus-like superfamily. Additionally, we found a novel interaction between the putative capping
and helicase-like portions of the BMV and CMV 1a proteins. Our
cumulative data suggest a working model for the assembly of the BMV RNA
replicase.
0022-538X/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.
Interactions between the Structural Domains of the
RNA Replication Proteins of Plant-Infecting RNA Viruses
*
Corresponding author. Mailing address: Department of
Biology, Indiana University, Bloomington, IN 47405. Phone: (812)
855-7959. Fax: (812) 855-6705. E-mail:
ckao{at}sunflower.bio.indiana.edu.
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