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1、Biochemistry1993,32,137-144137BetaineCanEliminatetheBasePairCompositionDependenceofDNAMelting7WilliamA.Rees,ThomasD.Yager,*JohnKorte,andPeterH.vonHippel’InstituteofMolecularBiologyandDepartmentofChemistry,UniversityofOregon,Eugene,Oregon97403ReceivedAugust7,199
2、2;RevisedManuscriptReceivedOctober28,1992ABSTRACT:Weshowthattheaminoacidanaloguebetaineshareswithsmalltetraalkylammoniumions[Melchior,W.B.,Jr.,&vonHippel,P.H.(1973)Proc.Nutl.Acud.Sci.U.S.A.70,298-3021theabilitytoreduceoreveneliminatethebasepaircompositiondepend
3、enceofDNAthermalmeltingtransitions.The“isostabilizing”concentrationofbetaine(atwhichATandGCbasepairsareequallystable)is-5.2M.Betaineexertsitsisostabilizingeffectwithoutappreciablyalteringtheconformationofdouble-strandedDNAfromtheBform.Thepresenceof>5Mbetaineals
4、odoesnotgreatlychangethebehaviorofDNAasapolyelectrolyte;thislackofeffectonelectrostaticinteractionsisexpectedbecausebetaineexistsasazwitterionnearneutralpH.StudyofDNAmeltingtransitionsinhighconcentrationsofbetainethusallowstheexperimentalseparationofcomposition
5、alandpolyelectrolyteeffectsonDNAmelting.Asaconsequence,betainesolutionscanalsobeusedtoinvestigateDNA-proteininteractionsunderisostabilizing(orclosetoisostabilizing)conditions,whichhasnotbeenpossibleusingisostabilizingsalts.Thispotentialisillustratedbyexaminingt
6、hehighlysaltconcentration-dependentinteractionofribonucleaseAwithDNAinconcentratedbetainesolutions.Thethermodynamicstabilityofdouble-strandednucleicAnearlyreport(Melchior&vonHippel,1973)describedacidshastwomajordeterminants.Thesearethepolyelec-aclassofsolventad
7、ditivesthatradicallyalteredthebasetrolyteeffect(Recordetal.,1978;Manning,1978;LeBretcomposition/sequenceeffectonnucleicacidstability.This&Zimm,1984)andthebasecompositionfsequenceeffectclassofadditivesconsistsofthetetraalkylammonium(TAA)(Breslaueretal.,1986;Frei
8、eretal.,1986).Detailedsaltsandtheircloserelatives.Itwasfound,forDNA,thatdifferencesbetweenbasepairsequencesareaveragedoutforthedependenceofTmonbasepaircompositioncouldbelong
