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Molecular and Cellular Biology, November 1998, p. 6525-6537, Vol. 18, No. 11
Graduate Program in Genetics and Molecular
Biology and Department of Biology, Emory University, Atlanta,
Georgia 30322
Received 22 June 1998/Returned for modification 5 August
1998/Accepted 19 August 1998
Mismatch repair (MMR) proteins actively inhibit recombination
between diverged sequences in both prokaryotes and eukaryotes. Although
the molecular basis of the antirecombination activity exerted by MMR
proteins is unclear, it presumably involves the recognition of
mismatches present in heteroduplex recombination intermediates. This
recognition could be exerted during the initial stage of strand
exchange, during the extension of heteroduplex DNA, or during the
resolution of recombination intermediates. We previously used an assay
system based on 350-bp inverted-repeat substrates to demonstrate that
MMR proteins strongly inhibit mitotic recombination between diverged
sequences in Saccharomyces cerevisiae. The assay system
detects only those events that reverse the orientation of the region
between the recombination substrates, which can occur as a result of
either intrachromatid crossover or sister chromatid conversion. In the
present study we sequenced the products of mitotic recombination
between 94%-identical substrates in order to map gene conversion
tracts in wild-type versus MMR-defective yeast strains. The sequence
data indicate that (i) most recombination occurs via sister chromatid
conversion and (ii) gene conversion tracts in an MMR-defective strain
are significantly longer than those in an isogenic wild-type strain.
The shortening of conversion tracts observed in a wild-type strain
relative to an MMR-defective strain suggests that at least part of the
antirecombination activity of MMR proteins derives from the blockage of
heteroduplex extension in the presence of mismatches.
0270-7306/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.
Mismatch Repair Proteins Regulate Heteroduplex
Formation during Mitotic Recombination in Yeast
*
Corresponding author. Mailing address: Department of
Biology, Emory University, 1510 Clifton Rd., Atlanta, GA 30322. Phone: (404) 727-6312. Fax: (404) 727-2880. E-mail:
jinks{at}biology.emory.edu.
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