1、See online version for legend and references.SnapShot:DNA Mismatch RepairAndres A.Larrea,Scott A.Lujan,and Thomas A.KunkelNational Institutes of Environmental Health Sciences,NIH,DHHS,Research Triangle Park,NC 27709,USA730 Cell 141,May 14,2010 2010 Elsevier Inc.DOI 10.1016/j.cell.2010.05.002730.e1 C
2、ell 141,May 14,2010 2010 Elsevier Inc.DOI 10.1016/j.cell.2010.05.002SnapShot:DNA Mismatch RepairAndres A.Larrea,Scott A.Lujan,and Thomas A.KunkelNational Institutes of Environmental Health Sciences,NIH,DHHS,Research Triangle Park,NC 27709,USAMismatch Repair in Bacteria and EukaryotesMismatch repair
3、in the bacterium Escherichia coli is initiated when a homodimer of MutS binds as an asymmetric clamp to DNA containing a variety of base-base and insertion-deletion mismatches.The MutL homodimer then couples MutS recognition to the signal that distinguishes between the template and nascent DNA stran
4、ds.In E.coli,the lack of adenine methylation,catalyzed by the DNA adenine methyltransferase(Dam)in newly synthesized GATC sequences,allows E.coli MutH to cleave the nascent strand.The resulting nick is used for mismatch removal involving the UvrD helicase,single-strand DNA-binding protein(SSB),and e
5、xcision by single-stranded DNA exonucleases from either direction,depending upon the polarity of the nick relative to the mismatch.DNA polymerase III correctly resynthesizes DNA and ligase completes repair.In bacteria lacking Dam/MutH,as in eukaryotes,the signal for strand discrimination is uncertai
6、n but may be the DNA ends associated with replication forks.In these bacteria,MutL harbors a nick-dependent endonuclease that creates a nick that can be used for mismatch excision.Eukaryotic mismatch repair is similar,although it involves several dif-ferent MutS and MutL homologs:MutS(MSH2/MSH6)reco
7、gnizes single base-base mismatches and 12 base insertion/deletions;MutS(MSH2/MSH3)recognizes insertion/deletion mismatches containing two or more extra bases.There are three eukaryotic MutL heterodimers:MutL(in humans MLH1/PMS2;in yeast MLH1/PMS1),MutL(MLH1/MLH3),and MutL(human MLH1/PMS1;yeast MLH1/
8、MLH2).The eukaryotic MutS and MutL heterodimers have partial overlap in substrate specificity.MutL and MutL have endonuclease activity,with the active sites present in human PMS2(yeast PMS1)and human MLH3.The resulting nick can be used for excision by the double-strand DNA 5-exonuclease activity of
9、Exo1.No helicase has yet been implicated in eukaryotic mismatch repair.Other exonucleases may perform excision,or the mismatch may be removed by strand displacement synthesis.DNA is resynthesized by DNA polymerase.Protein StructuresAlso depicted are structures of proteins involved in DNA mismatch re
10、pair(including Protein Data Bank ID,resolution,and species)among the many that are now available.Future studies will likely add to this list,possibly including proteins involved in excision,termination,and coordination of mismatch repair with nucleosome reloading and chromatin remodeling after repli
11、cation.Evolutionary ConservationThe table provides information on the evolutionary conservation of mismatch repair proteins.Additional notes:grey icons indicate genes found only in subset of species;MSH1 in fungi is involved in mitochondrial DNA repair and is derived from-proteobacterial MutS via ho
12、rizontal gene transfer from ancestral mitochondria;MutS in plants is derived from cyanobacterial MutS,is associated with chloroplasts,and is present in varying copy numbers;in archaea the general mismatch repair pathway is unknown,although MutS and MutL family members are found in limited species,li
13、kely due to horizontal gene transfer from bacteria.For archaeal MutS5,no mismatch repair-specific DNA binding has been reported.AcknowledgmentsWe would like to thank D.Erie and P.Hsieh for critical review and suggestions.A.A.L.and S.A.L.contributed equally to this work.RefeRencesAcharya,S.,Foster,P.
14、,Brooks,P.,and Fishel,R.(2003).The coordinated functions of the E.coli MutS and MutL proteins in mismatch repair.Mol.Cell 12,233246.Allen,D.,Makhov,A.,Grilley,M.,Taylor,J.,Thresher,R.,Modrich,P.,and Griffith,J.(1997).MutS mediates heteroduplex loop formation by a translocation mechanism.EMBO J.16,44
15、674476.Harfe,B.,and Jinks-Robertson,S.(2000).DNA mismatch repair and genetic instability.Annu.Rev.Genet.34,359399.Hsieh,P.,and Yamane,K.(2009).DNA mismatch repair:Molecular mechanism,cancer,and aging.Mech.Ageing Dev.129,391407.Iyer,R.R.,Pluciennik,A.,Burdett,V.,and Modrich,P.L.(2006).DNA mismatch re
16、pair:functions and mechanisms.Chem.Rev.106,302323.Kadyrov,F.,Genshel,J.,Fang,Y.,Penland,E.,Edelmann,W.,and Modrich,P.(2009).A possible mechanism for exonuclease 1-independent eukaryotic mismatch repair.Proc.Natl.Acad.Sci.USA 106,84958500.Kolodner,R.D.,and Marisischky,G.T.(1999).Eukaryotic DNA mismat
17、ch repair.Curr.Opin.Genet.Dev.9,8996.Kunkel,T.,and Erie,D.(2005).DNA mismatch repair.Annu.Rev.Biochem.74,681710.Li,G.(2008).Mechanisms and functions of DNA mismatch repair.Cell Res.18,8591.Lin,Z.,Nei,M.,and Ma,H.(2007).The origins and early evolution of DNA mismatch repair genes multiple horizontal gene transfers and co-evolution.Nucleic Acids Res.35,75917603.
