Mismatch repair inhibits homeologous recombination via coordinated directional unwinding of trapped DNA structures.
Homeologous recombination between divergent DNA sequences is inhibited by DNA mismatch repair. In Escherichia coli, MutS and MutL respond to DNA mismatches within recombination intermediates and prevent strand exchange via an unknown mechanism. Here, using purified proteins and DNA substrates, we find that in addition to mismatches within the heteroduplex region, secondary structures within the displaced single-stranded DNA formed during branch migration within the recombination intermediate are involved in the inhibition. We present a model that explains how higher-order complex formation of MutS, MutL, and DNA blocks branch migration by preventing rotation of the DNA strands within the recombination intermediate. Furthermore, we find that the helicase UvrD is recruited to directionally resolve these trapped intermediates toward DNA substrates. Thus, our results explain on a mechanistic level how the coordinated action between MutS, MutL, and UvrD prevents homeologous recombination and maintains genome stability.
Department of Genetics, Cancer Genomics Netherlands, Erasmus Medical Center, Rotterdam 3000 CA, The Netherlands.
Khek-Chian
KC
Tham
Nicolaas
N
Hermans
Herrie H K
HH
Winterwerp
Michael M
MM
Cox
Claire
C
Wyman
Roland
R
Kanaar
Joyce H G
JH
Lebbink
D000251:Adenosine Triphosphatases / Q000378:metabolism*; D004265:DNA Helicases / Q000378:metabolism*; D053843:DNA Mismatch Repair; D004269:DNA, Bacterial / Q000235:genetics* / Q000378:metabolism*; D004277:DNA, Single-Stranded / Q000378:metabolism; D004926:Escherichia coli / Q000235:genetics; D029968:Escherichia coli Proteins / Q000378:metabolism*; D014644:Genetic Variation; D059765:Homologous Recombination / Q000235:genetics*; D000070956:MutL Proteins; D051719:MutS DNA Mismatch-Binding Protein / Q000378:metabolism*; D011938:Rec A Recombinases / Q000378:metabolism
D004269:DNA, Bacterial; D004277:DNA, Single-Stranded; D029968:Escherichia coli Proteins; C074770:MutL protein, E coli; D011938:Rec A Recombinases; D000251:Adenosine Triphosphatases; C506746:UvrD protein, E coli; D000070956:MutL Proteins; D051719:MutS DNA Mismatch-Binding Protein; D004265:DNA Helicases