Removal of Contaminating Genomic DNA in QRT-PCR Using a … · 2009. 10. 27. · Thermo...
Transcript of Removal of Contaminating Genomic DNA in QRT-PCR Using a … · 2009. 10. 27. · Thermo...
Conclusion• Thecurrentdatasuggestthatshrimpnucleasehasnoinhibitoryeffecton1-stepor2-stepQRT-
PCRandtheintegrityofRNAandcDNAisnotaltered.
• ShrimpnucleaseeffectivelyremovesanycontaminatingDNAwithoutaddinganextrasteptotheQRT-PCRprotocol;thus,completelyeliminatingtheneedforharshandtime-consumingDNaseItreatment.Indoingso,shrimpnucleaseincreasestheaccuracyandreproducibilityofQRT-PCRreactions,especiallywhenusingcrudelypurifiedsamples.
• Shrimpnucleasecanalsobeusedforremovalofampliconcarry-overcontaminantsinthePCRreaction.
† For more information contact [email protected]
IntroductionDNAcontaminationcanoftenoccurinquantitativereversetranscription–polymerasechainreactions(QRT-PCR),andshouldberemovedinordertoavoidfalsepositiveresults.DNaseIiscommonlyusedforremovingDNAcontamination,butthishasarelativelylongandharshprotocolwhichintroducesanextrastepbetweentheisolationofRNAandtheQRT-PCRreactionitself,aswellasincreasingtheriskofRNAdegradationduetotheharshinactivationconditions.
AnendonucleasefromarcticshrimpPandalus borealishaspropertiesthatmakeitusefulfortheremovalofcontaminatingDNA.TheendonucleaseactivityoftheenzymeisspecifictodoublestrandedDNA,whichthereforeallowstheenzymetobeaddeddirectlyintothereversetranscriptionstep.UnlikeDNaseI,theshrimpnucleaseiseasilyinactivatedathightemperatures,suchasthoseusedfortheRTdeactivation/hotstartincubationstepofaQRT-PCRreaction,andthereforecanbeusedtoselectivelydegradedoublestrandedDNA,leavingsinglestrandedDNAandRNAintact.
AimTodeterminewhetheradditionofshrimpnucleasecanremovethecontaminatingDNAfromtheQRT-PCRreactionwithouthavinganyinhibitoryeffects.
MethodToevaluatewhetherThermoScientificshrimpnuclease(AB-1311)wouldinhibitQRT-PCRreaction,0.1,0.2and0.4unitsoftheenzymewereadded/reaction,inconjunctionwithotherreagentsfromtheThermoScientificVerso™ QRT-PCR Kit(AB-4100).Five10-folddilutions(100ng,10ng,1ng,100pgand10pg)ofHumanLiverTotalRNA(AmbionEuropeLtd,Huntingdon)wereusedastemplatetoamplify74bpfragmentofApolipoprotein-BgeneusingaStratageneMx3005PQPCRinstrument(Stratagene,Leicester).
TotesttheabilityofshrimpnucleasetoeffectivelyeliminatecontaminatingDNA,0.4unitsofshrimpnucleasewerepre-incubatedwithfour10-folddilutions(100,10,1and0.1ng)ofhumangenomicDNA(Sigma-Aldrich,Dorset)at50°Cfor30minpriortotheQPCRreaction.Amplificationofapolipoprotein-Bgene(74bp)wascarriedoutonStratageneMx3005PQPCRinstrumentusingThermoScientificABsolute™BlueQPCRProbeMix(AB-4132).Asacontrol,alltemplatedilutionswereincubatedwithshrimpnucleasebufferwithouttheenzyme.ThepercentageremovalofgenomicDNAwascalculatedbycomparingthe∆CTvaluesbetweenreactionswhereDNAwaspre-incubatedwithshrimpnucleasetoreactionsincubatedwithbuffer.Allexperimentswereperformedthreetimeswithtriplicatereactions.
ResultsFigure1showsthatadditionofshrimpnuclease(0.1to0.4units)intheQRT-PCRreactionmixhadnoadverseeffectsontheintegrityofRNA.InadditiontheresultconfirmedthatamplificationofApolipoproteinBgeneacrossfive10-folddilutionsofRNAwasnotinhibitedbyanyofthethreeconcentrationsofshrimpnucleasetestedfortheseexperiments(Figure1).Table1andFigure2showthatpre-QPCRincubationof100,10,1and0.1ngofhumangenomicDNAwith0.4unitsofshrimpnucleasecausedretardationofCTvaluesintestsamplescomparedtothecontrols(bufferonlywithouttheshrimpnuclease).AlateCTvalueisindicativeoflowquantitiesofthestartingtemplate.Anotable99-100%removalofDNAfollowingincubationwith0.4unitsofshrimpnucleasevalidatesefficacyofthisenzymetoeliminatecontaminatingDNAfromQRT-PCRreactions(Table1andFigure2).
Removal of Contaminating Genomic DNA in QRT-PCR Using a Shrimp Nuclease
NickyQuispe,SaimaNaveedNayabandIanKavanagh†
ThermoFisherScientific,ABgeneHouse,BlenheimRoad,Epsom,Surrey,KT199AP,UnitedKingdom.
Figure 2:HumangenomicDNA(100-0.1ng)waspre-incubatedwith0.4units/reactionofshrimpnuclease(redcurves)andwiththebufferonly(blackcurves)beforeamplificationofa74bpfragmentoftheApolipoproteinBgeneonStratageneMx3005P.Figure 1:1-stepQRT-PCR
resultsshowingamplificationofApolipoprotein-Bgeneusing100ng-10pgofinputHumanLiverTotalRNAfollowingincubationwith0.1(green),0.2(blue),0.4(red)unitsofshrimpnucleaseperreaction.Blackcurvesrepresentwaterasacontrolusedinsteadoftheshrimpnuclease.
DNA (ng) CT control(buffer only)
CT test(Shrimp Nuclease)
ΔCT Calculated remaining concentration of DNA after incubation with shrimp nuclease (ng)
% Removal
100 21.89 29.93 -8.04 0.365 99.64
10 25.12 32.69 -7.57 0.055 99.45
1 28.27 37.17 -8.9 0.003 99.75
0.1 31.54 NoCT - - 100
NTC NoCT NoCT - - n/a
Table 1:RemovalofDNAfollowingincubationwithshrimpnuclease