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J. Virol., 01 1995, 131-140, Vol 69, No. 1
PD Nagy and JJ Bujarski
Brome mosaic virus (BMV), a tripartite positive-stranded RNA virus of
plants engineered to support intersegment RNA recombination, was used for
the determination of sequence and structural requirements of homologous
crossovers. A 60-nucleotide (nt) sequence, common between wild-type RNA2
and mutant RNA3, supported efficient repair (90%) of a modified 3'
noncoding region in the RNA3 segment by homologous recombination with
wild-type RNA2 3' noncoding sequences. Deletions within this sequence in
RNA3 demonstrated that a nucleotide identity as short as 15 nt can support
efficient homologous recombination events, while shorter (5-nt) sequence
identity resulted in reduced recombination frequency (5%) within this
region. Three or more mismatches within a downstream portion of the common
60-nt RNA3 sequence affected both the incidence of recombination and the
distribution of crossover sites, suggesting that besides the length, the
extent of sequence identity between two recombining BMV RNAs is an
important factor in homologous recombination. Site-directed mutagenesis of
the common sequence in RNA3 did not reveal a clear correlation between the
stability of predicted secondary structures and recombination activity.
This indicates that homologous recombination does not require similar
secondary structures between two recombining RNAs at the sites of
crossovers. Nearly 20% of homologous recombinants were imprecise
(aberrant), containing either nucleotide mismatches, small deletions, or
small insertions within the region of crossovers. This implies that
homologous RNA recombination is not as accurate as proposed previously. Our
results provide experimental evidence that the requirements and thus the
mechanism of homologous recombination in BMV differ from those of
previously described heteroduplex-mediated nonhomologous recombination (P.
D. Nagy and J. J. Bujarski, Proc. Natl. Acad. Sci. USA 90:6390-6394, 1993).
Copyright © 1995, American Society for Microbiology
Efficient system of homologous RNA recombination in brome mosaic virus: sequence and structure requirements and accuracy of crossovers
Plant Molecular Biology Center, Northern Illinois University, De Kalb 60115.
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