title: MutS mediates heteroduplex loop formation by a translocation mechanism.
abstract: Interaction of Escherichia coli MutS and MutL with heteroduplex DNA has been visualized by electron microscopy. In a reaction dependent on ATP hydrolysis, complexes between a MutS dimer and a DNA heteroduplex are converted to protein-stabilized, alpha-shaped loop structures with the mismatch in most cases located within the DNA loop. Loop formation depends on ATP hydrolysis and loop size increases linearly with time at a rate of 370 base pairs/min in phosphate buffer and about 10,000 base pairs/min in the HEPES buffer used for repair assay. These observations suggest a translocation mechanism in which a MutS dimer bound to a mismatch subsequently leaves this site by ATP-dependent tracking or unidimensional movement that is in most cases bidirectional from the mispair. In view of the bidirectional capability of the methyl-directed pathway, this reaction may play a role in determination of heteroduplex orientation. The rate of MutS-mediated DNA loop growth is enhanced by MutL, and when both proteins are present, both are found at the base of alpha-loop structures, and both can remain associated with excision intermediates produced in later stages of the reaction.
authors.affiliation: Department of Biochemistry, Duke University Medical Center, Durham, NC 27710, USA.
authors.forename: D J
authors.initials: DJ
authors.lastname: Allen
authors.forename: A
authors.initials: A
authors.lastname: Makhov
authors.forename: M
authors.initials: M
authors.lastname: Grilley
authors.forename: J
authors.initials: J
authors.lastname: Taylor
authors.forename: R
authors.initials: R
authors.lastname: Thresher
authors.forename: P
authors.initials: P
authors.lastname: Modrich
authors.forename: J D
authors.initials: JD
authors.lastname: Griffith
mesh_terms: D000251:Adenosine Triphosphatases; D000255:Adenosine Triphosphate / Q000378:metabolism; D001426:Bacterial Proteins / Q000737:chemistry / Q000378:metabolism*; D004260:DNA Repair; D004279:DNA, Viral / Q000235:genetics / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism; D015252:Deoxyribonucleases, Type II Site-Specific / Q000378:metabolism; D019281:Dimerization; D004587:Electrophoresis, Agar Gel; D004926:Escherichia coli / Q000737:chemistry / Q000235:genetics*; D029968:Escherichia coli Proteins; D007700:Kinetics; D008854:Microscopy, Electron; D000070956:MutL Proteins; D051719:MutS DNA Mismatch-Binding Protein; D009690:Nucleic Acid Conformation; D009692:Nucleic Acid Heteroduplexes / Q000737:chemistry / Q000378:metabolism* / Q000648:ultrastructure; D011487:Protein Conformation
chemical_list: D001426:Bacterial Proteins; D004279:DNA, Viral; D004268:DNA-Binding Proteins; D029968:Escherichia coli Proteins; C074770:MutL protein, E coli; D009692:Nucleic Acid Heteroduplexes; D000255:Adenosine Triphosphate; C067043:endodeoxyribonuclease NheI; D015252:Deoxyribonucleases, Type II Site-Specific; D000251:Adenosine Triphosphatases; D000070956:MutL Proteins; D051719:MutS DNA Mismatch-Binding Protein; C497175:MutS protein, E coli