Protein roadblocks and helix discontinuities are barriers to the initiation of mismatch repair

The hemimethylated d(GATC) sequence that directs Escherichia coli mismatch repair can reside on either side of a mismatch at a separation distance of 1,000 bp or more. Initiation of repair involves the mismatch-, MutS-, and MutL-dependent activation of MutH endonuclease, which incises the unmethylat...

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Bibliographic Details
Published in:Proceedings of the National Academy of Sciences - PNAS 2007-07, Vol.104 (31), p.12709-12713
Main Authors: Pluciennik, Anna, Modrich, Paul
Format: Article
Language:English
Subjects:
Bacteriophages
Base pair mismatch
Base Sequence
Biochemistry
Biological Sciences
Deoxyribonuclease EcoRI - genetics
Deoxyribonuclease EcoRI - metabolism
Dimers
DNA
DNA - chemistry
DNA Helicases - metabolism
DNA Mismatch Repair
DNA repair
E coli
Enzyme Activation
Enzymes
Escherichia coli
Genetics
Glutamic Acid - genetics
Glutamic Acid - metabolism
Molecules
Mutation - genetics
Nucleic acid heteroduplexes
Oligonucleotides
Proteins
rev genes
Signal transduction
Substrate Specificity
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Summary:The hemimethylated d(GATC) sequence that directs Escherichia coli mismatch repair can reside on either side of a mismatch at a separation distance of 1,000 bp or more. Initiation of repair involves the mismatch-, MutS-, and MutL-dependent activation of MutH endonuclease, which incises the unmethylated strand at the d(GATC) sequence, with the ensuing strand break serving as the loading site for the appropriate 3'-to-5' or 5'-to-3' excision system. However, the mechanism responsible for the coordinated recognition of the mismatch and a hemimodified d(GATC) site is uncertain. We show that a protein roadblock (EcoRIE₁₁₁Q, a hydrolytically defective form of EcoRI endonuclease) placed on the helix between the two DNA sites inhibits MutH activation by 70-80% and that events that escape inhibition are attributable, at least in part, to diffusion of EcoRIE₁₁₁Q away from its recognition site. We also demonstrate that a double-strand break located within the shorter path linking the mismatch and a d(GATC) site in a circular heteroduplex abolishes MutH activation, whereas a double-strand break within the longer path is without effect. These findings support the idea that initiation of mismatch repair involves signaling along the helix contour.
ISSN:0027-8424
1091-6490
DOI:10.1073/pnas.0705129104