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Journal of Virology, November 1998, p. 9192-9200, Vol. 72, No. 11
Institute of Bioorganic Chemistry, Polish
Academy of Sciences, Poznan, Poland1;
Department of Biochemistry and Molecular Biology, University of
Massachusetts, Amherst, Massachusetts 010032;
Department of Biology, Indiana University, Bloomington,
Indiana 474053; and
Plant Molecular
Biology Center and Department of Biological Sciences, Northern
Illinois University, De Kalb, Illinois 601154
Received 2 February 1998/Accepted 18 July 1998
Previously, we have observed that mutations in proteins 1a and 2a,
the two virally encoded components of the brome mosaic virus (BMV)
replicase, can affect the frequency of recombination and the locations
of RNA recombination sites (P. D. Nagy, A. Dzianott, P. Ahlquist,
and J. J. Bujarski, J. Virol. 69:2547-2556, 1995; M. Figlerowicz, P. D. Nagy, and J. J. Bujarski, Proc. Natl.
Acad. Sci. USA 94:2073-2078, 1997). Also, it was found before that the N-terminal domain of 2a, the putative RNA polymerase protein, participates in the interactions between 1a and 2a (C. C. Kao, R. Quadt, R. P. Hershberger, and P. Ahlquist, J. Virol.
66:6322-6329, 1992; E. O'Reilly, J. Paul, and C. C. Kao, J. Virol. 71:7526-7532, 1997). In this work, we examine how mutations
within the N terminus of 2a influence RNA recombination in BMV. Because
of the likely electrostatic character of 1a-2a interactions, five 2a
mutants, MF1 to MF5, were generated by replacing clusters of acidic
amino acids with their neutral counterparts. MF2 and MF5 retained
nearly wild-type levels of 1a-2a interaction and were infectious in
Chenopodium quinoa. However, compared to that in wild-type
virus, the frequency of nonhomologous recombination in both MF2 and MF5
was markedly decreased. Only in MF2 was the frequency of homologous
recombination reduced and the occurrence of imprecise homologous
recombination increased. In MF5 there was also a 3' shift in the
positions of homologous crossovers. The observed effects of MF2 and MF5
reveal that the 2a N-terminal domain participates in different ways in homologous and in nonhomologous BMV RNA recombination. This work maps
specific locations within the N terminus involved in 1a-2a interaction
and in recombination and further suggests that the mechanisms of the
two types of crossovers in BMV are different.
0022-538X/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.
Mutations in the N Terminus of the Brome Mosaic
Virus Polymerase Affect Genetic RNA-RNA Recombination
*
Corresponding author. Mailing address: Plant Molecular
Biology Center, Northern Illinois University, Montgomery Hall, De Kalb, IL 60115. Phone: (815) 753-0601. Fax: (815) 753-7810. E-mail: jbujarski{at}niu.edu.
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