SnapShot:TheReplisomeNinaY.YaoandMikeO’DonnellTheRockefellerUniversityandHHMI,NewYork,NY10065,USASeeonlineversionforlegendandreferences.1088Cell141,June11,2010©2010ElsevierInc.DOI10.1016/j.cell.2010.05.042SnapShot:TheReplisomeNinaY.YaoandMikeO’DonnellTheRockefellerUniversityandHHMI,NewYork,NY10065,USA1088.e1Cell141,June11,2010©2010ElsevierInc.DOI10.1016/j.cell.2010.05.042Inallorganisms,successfulcelldivisionrequiresaccuratecopyingofchromosomalDNA.Toduplicatetheirgenomes,allcellsuseamultiproteinapparatusknownastherepli-some(reviewedbyBenkovicetal.,2001;McHenry,2003;YaoandO’Donnell,2009).Thefundamentalcomponentsofthereplisomeareconservedacrossviruses,bacteria,archaea,andeukaryotes(Table).Theyincludeahelicasetounwindthedouble-strandedDNA,apolymerase(s)tosynthesizenewstrandsofDNA,andaclamploadertoorganizethecomplexontheDNA.ThereplisomeassembliesataregionoftheDNA,calledthereplicationfork,wherethedouble-strandedDNAisseparatedintotwoindividualstrands,whicharebothsubsequentlycopiedinthe5′to3′directionoftheDNA.InthisSnapShot,wecomparethespecificcomponentsofthereplisomeinEscherichiacoliwiththoseofthereplisomeineukaryotes.Inaddition,wedescribehowthelaggingstrandissynthesizedfromOkazakifragments.BacterialReplisomeAtthefrontoftheE.colireplisome,thehexamericDnaBproteinencirclesonestrandofDNA.ThishelicaseusestheenergyofATPhydrolysistoseparatetheduplexDNAintotwodaughterstrandsbytranslocating5′to3′alongthestrandwithinitscentralpore.Single-strandDNA-binding(SSB)proteinscoateachindividualstrandtoremoveDNAsecondarystructuresthatwouldimpedereplication.DNApolymerase(Pol)III,oneproteincomplexoneachdaughterstrand,thenusesthissingle-strandedDNAasatemplatetosynthesizeacomplementarystrand.PolIIIhashighfidelity,withanerrorrateofapproximatelyonemutationforeach10−5to10−6basesreplicated.However,ifPolIIImistakenlyincorporatesanincorrectnucleotide,aproofreading3′to5′exonucleasewithinthepolymeraseremovestheincorrectnucleotide.Theβclamp,adimericring(panelC),tethersPolIIItotheDNAanden...
