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J. Bacteriol., Apr 1995, 1692-1698, Vol 177, No. 7
Z Silberstein, Y Tzfati and A Cohen
Alternative models for break-induced recombination predict different
distributions of primary products. The double-stranded break-repair model
predicts a noncrossover product and equimolar amounts of two crossover
products. The one-end pairing model predicts two crossover products, but
not necessarily in equimolar amounts, and the single- stranded annealing
model predicts deletion of the fragment between the pairing sequences.
Depending on the structure of the recombining substrate(s) and the nature
of the resectioning step that precedes strand annealing, the
single-stranded annealing mechanism would yield only one or both crossover
products. We tested these predictions for the RecE recombination pathway of
Escherichia coli. Nonreplicating intramolecular recombination substrates
with a double-stranded break (DSB) within one copy of a direct repeat were
released from chimera lambda phage by in vivo restriction, and the
distribution of primary circular recombination products was determined.
Noncrossover products were barely detectable, and the molar ratio of the
two crossover products was proportional to the length ratio of the
homologous ends flanking the DSB. These results suggest an independent
pairing of each end with the intact homolog and argue against the
double-stranded break- repair model. However, the results do not
distinguish alternative pairing mechanisms (strand invasion and strand
annealing). The kinetics of heteroduplex formation and heteroduplex strand
polarity were investigated. Immediately following the DSB induction,
heteroduplex formation was done by pairing the strands ending 3' at the
break. A slow accumulation of the complementary heteroduplex made by the
pairing of the strands ending 5' at the break (5' heteroduplexes) was
observed at a larger stage.(ABSTRACT TRUNCATED AT 250 WORDS)
Copyright © 1995, American Society for Microbiology
Primary products of break-induced recombination by Escherichia coli RecE pathway
Department of Molecular Genetics, Hebrew University-Hadassah Medical School, Jerusalem, Israel.
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