MakinglibraryDNAfromtheDNAwesendyou
ThelibraryisdistributedasindividualpoolsintheformofDNA.Youwillbesentaboutamicrogramofeachpoolavailable.TransformasuitableamountintoE.coli(anystrainsuitableformakingplasmidpreps).Selecttransformantswith40ug/mlkanamycinand/or50ug/mlampicillin.Obtain50,000coloniesforeachpool.ElutecoloniesfromplatesinLB;makea-70Cstockofthiseluate.DiluteeluateintoLBplusantibiotictogiveaculturewithanalmostsaturateddensity.Growat37Cforafewhours.MakeminiprepormidiprepDNA.
TransformingyeastwithDNAfromtheinsertionlibrary
OVERVIEW:MutagenizedDNAfromthelibraryisexcisedfromthebacterialvector.Itisthentransformedintoaleu2strainofyeast.Thisprocedureisoutlinedinthisfigure.Useofacircle-zerostrainwillpreventrecoveryofinsertionsinthe2-micronplasmid.Thebeststrategyistoscreenafewthousandtransformantsfromeachpool.Screening30,000transformantsshouldgiveyou95%coverageoftheyeastgenome.
Tominimizedoubleintegrants,transformationsshouldcontainthelowestamountofDNApracticable.Wethereforerecommendthatapilotexperimentbeperformedtodeterminetransformationefficiencyofthestrain,andconditionsthenbescaledupasappropriate.ThepilotprotocolgivenbelowusesamodifiedversionofthemethodofChenetal.(1992).Youshouldusewhatevertransformationprotocolworksbestinyourhands.
- PlasmidDNAfrompoolsofthemTn3-mutagenizedgenomiclibraryisdigestedwithNotI.A2.1-kbbandfromthevectorshouldbeapparent,togetherwitharangeofbandsinthe8-kbregion.
- A10-mlcultureoftheyeasthoststrainisgrowntoadensityof107cells/ml(O.D.600of1).Useofsuchlogarithmically-dividingculturesincreasestransformationefficiency.
- Cellsarepelletedandwashedoncewith5volumesofOneStepbuffer(0.2MLiAc,40%PEG4000,100mMbeta-mercaptoethanol).Thiswashisespeciallyimportantwhenculturevolumesareincreased.
- CellsareresUSPendedin1mlofOneStepbuffercontaining1mgofdenaturedsalmonspermDNA.100ulaliquotsofthissuspensionarethenaddedtotubescontainingfrom0.1to1ugofNotIdigestedplasmidDNA.
- Tubesarevortexedtomixthecontentsthoroughly,thenincubatedat45ofor30minutes.
- Cellsarepelletedandresuspendedin400ulofSC-leu.200ulisplatedontoSC-leumedium.Platesareincubatedat30oCfor3to4days.
ScreeningforgeneexpressionusinglacZfusions
OVERVIEW:Transformantstrainscarryingin-framefusionsbetweenyeastgenesandlacZareidentifiedbyacolorassayforbeta-galactosidaseactivity.
- TomaximizedetectionoflacZfusionsexpressedatalowlevel,transformantcoloniesarepatchedtoYPADplatesatadensityof100perplate.
- Toidentifyvegetativelyexpressedgenes,cellsarereplicaplatedtoanSC-leuplateonwhichasterilediscofWhatman1Afilterpaperhasbeenplaced,andgrownovernightat30oC.Othermediaorgrowthconditionscanbesubstitutedasdesired.Forade2strains,anytestmediashouldcontain80mg/lofadenine.
- Filtersareliftedfromtheplatesandplacedinthelidofa9-cmglasspetridish.Thislidisthenplacedinsideaclosed15-cmglasspetridishcontainingchloroformfor10to30minutes.Theminimumexposuretimenecessaryforaparticularyeaststraincanbedeterminedempirically.
- Filtersareplacedcolony-sideupontoX-Galplates(120ug/ml5-bromo-4-chloro-3-indolyl-beta-D-galactopyranoside,0.1MNaPO4[pH7]and1mMMgSO4in1.6%agar)andincubatedat30oCforupto2days.Theseplatescanbeverythin;theiruseincreasesthesignaloverthatobtainedbysimplysoakingthefiltersinabufferedX-galsolution.
- TransformantscarryingproductivelacZfusionsarerecoveredfromtheregrownYPADplates.ItisadvisabletosubsequentlymaintainselectionforLEU2whereverpossIBLe,assomemutationsaredeleteriousevenintheheterozygousstate.
Identificationofthegenomicsiteoftransposoninsertion
OVERVIEW:Todeterminethesiteoftransposoninsertion,genomicDNAimediatelyadjacenttothelacZsequencesisrescuedinEscherischiacoli.Tointroduceanoriginofreplication(ori),aplasmidmarkedwithURA3(pRSQ2-URA3,U64694)replacespartofthetransposonbyrecombinationbetweenplasmid-andtransposon-bornecopiesoflacZsequences.Thisprocedureisoulinedinthisfigure.YeastDNAisrecoveredfromthesetransformantsandcutwitha"recovery"enzyme(EcoRI,HindIIIEcoRV,PstI,ClaI,SalI,XhoI,KpnI).Thisreleasesasalinearsegmentthebacterialoriginofreplication,thebeta-lactamasegeneandaportionofthelacZgenewithadjacentyeastDNA;thisfragmentisthencircularizedandrecoveredinbacteria.pRSQ2ishighcopynumberinE.coli.Plasmidsaresequencedusingaprimercomplementarytothe5"endofthetransposon.Thisprocessrequiresthethreeprotocolsgivenbelow.
Alternativemethod:C.Friddle(http://genome-www.stanford.edu/group/botlab)hasdevelopedavectorettePCRrescueprotocolforlacZ-basedtransposons.
CAUTION!Twoormoreinsertioneventsmayhaveoccurredinupto10%ofthepopulation.Thesecanbeidentifiedbyexaminationofsegregationofthetransposon-borneLEU2Markerupontetraddissection.YoushouldbesurethatthestrainhasonlyonetransposonbeforeproceedingtorecoveringaplasmidcontaininggenomicDNA.Ifyouhaveusedthelibraryformutagenesis,youarestronglyadvisedtomakesurethatyourphenotypeislinkedtothetransposoninsertion,sincespontaneousmutationscanariseatothersites.Youcanwastetimerecoveringjunkifyoudon"tcheck.
Transformationofyeaststrains
Wesuggesttransformingtheyeastwith1-5ugofBamHI-digestedpRSQ2-URA3plasmidDNA,selectingthetransformantsonSC-leu-ura.Thisisatargettedreplacement,soefficiencywilldependonyourstrain.ThemethodofChenetal.(1992)givenabovecanbeused.IfanampRplasmidispresentintheyeaststraintobetransformed,adifferentmarkercouldbeclonedintothepRSQ2polylinkertoenableitsrecovery.
RecoveryofgenomicDNAfromyeaststrains
ForadetaileddiscussionofgenomicDNApreparationfromyeast,seePhilippsenetal.(1991).Hereisthemethodthatweuse.
- Yeaststrainsaregrowntosaturationat30oCin2mlofYPAD.Wesuggestusingacoupleoftransformantsforeachstrain.
- Cellsarerecoveredbycentrifugationat13,000r.p.m.for1minute.Thesupernatantisremovedbyaspirationandcellsareresupendedin250ulof0.1MEDTA(pH7.5),14mMbeta-mercaptoethanolcontaining150ug/mlzymolyase.Cellsareincubatedat37oCuntilspheroplasted.Overspheroplastingdoesnotaffectrecovery.
- 50ulofminiprepmix(0.25MEDTA(pH8.5),0.5MTrisbase,2.5%SDS)isaddedtoeachtube.Samplesaremixedbyinversion,thenincubatedinawaterbathat65oCfor30minutes.
- 63ulof5MKAcisaddedtoeachsample.Samplesaremixedbyinversionandincubatedonicefor30minutes.
- Samplesarespunat13000r.p.m.inamicrofugefor10minutes.Supernatantsaretransferredbypouringeachsampleintoanewtubecontaining720ulof100%ethanol.ADNAprecipitateshouldbevisible.Samplesaremixedbyinversionandspunfor5minutesasabove.
- Tubesaredrainedthoroughly,and130ulTEcontaining1mg/mlRNAaseAisaddedtotheundriedpellets.ResupensionofDNAisgradualandoccursduringsubsequentincubationat37oCfor35minuteswithoccasionalvortexing,DNAisreprecipitatedbyadditionof130ulofisopropanol.Samplesaremixedbyinversionandspunfor5minutesasabove.
- Tubesaredrained.A70%ethanolwashmaybeperformedtoremovesalt.Finally,pelletsareairdriedandresupendedin40ulofTEwithincubationat37oC.About10ugofgenomicDNAisobtained.
Plasmidrescue
- 5ugofyeastgenomicDNAisdigestedovernightat37oCwith5unitsof"recovery"enzyme(EcoRI,HindIII,SalI,EcoRV,PstI,ClaI,XhoI,orKpnI)inatotalvolumeof40ul.
- 20ulofthesampleisrunonageltocheckdigestion.ThisgelmayalsobeusedforSouthernanalysis(seebelow).Theremainderisheatedto65oCfor25minutestoinactivatetherestrictionenzyme,and215ulofH2O,25ulof10Xligasebufferand1ulofligase(400units)areadded.Tofavourintramolecularreactions,theDNAconcentrationintheligationshouldnotbeover10ug/ml,andcanbeaslowas2ug/ml.
- Afterligationat16oCfor4to16hours,DNAisprecipitatedbyadditionof125ulof7.5MNH4Acand375ulofisopropanolandrecoveredbycentrifugationat2190g(ormore)for20minutes.
- TheDNApelletiswashedoncewith70%ethanol,thenresuspendedin6-20ulofTE.3ulofthisistransformedintoE.coli,(weuseelectroporation)selectingforampicillinresistance.Dominiprepsofseveralcoloniesforeachstrain.
- Rescuedplasmidscanbeanalyzedbydouble-digestionwithBamHIandthe"recovery"enzyme.Desiredplasmidsdisplaya2.85-kbbandcontainingvectorsequences(seeFigure1b)plusadditionalband(s)fromgenomicDNA.Ifyouget"mystery"plasmids,tryadifferenttransformant/recoveryenzyme.
- DNApreparationsmaybesequencedusingaprimerfromlacZsequencesinsidetheterminalrepeat,egthe-40primer(#1212,NewEnglandBiolabs).Onlytrustyoursequenceuptothefirstsitefortherecoveryenzyme,asotherfragmentscangetclonedinduringcircularization.
SequenceoflacZendofmTn3-lacZ/LEU2:
Bases1-38aretheterminalrepeat,alsopresentonthevector.
GGGGTCTGACGCTCAGTGGAACGAAAACTCACGTTAAGggggATCCCGTCGTTTTACAACGTCGTGACTGGGAAAACCCTGCGTTACCCAACTTAATCG
TheaccessionnumberformTn-lacZ/LEU2isU35112.
TheaccessionnumberforpRSQ2-URA3isU64694.
Alternativerescuestrategies
pRSQ
- DiagramoutlininguseofpRSQ
- U34887,GenbankentryforpRSQ
YIp5
- DiagramoutlininguseofYIp5
- L09157,GenbankentryforYIp5
VectorettePCR
CarlFriddlehasdevelopedavectorettePCRprotocolforidentifyingthesiteofinsertion.Thiscanbefoundathttp://genome-www.stanford.edu/group/botlab/protocols/vectorette.html.
Transferringthedisruptionalleletootherstrains:
WhenpRSQ2-URA3integratesintothetransposonitcreatesan11.7kbinsertion.Thiselementisnotcleavedbythefollowingenzymes:AvrII,BglII,BspEI,EagI,MscI,NaeI,NheI,NruI,NotI,PmlI,SmaI,SnABI,SpeI,SphI,XmaI.Theseenzymescanthereforebeusedtorecoveralargeplasmidcontainingsequencesboth5"and3"tothetransposoninsertion.Wehavesuccessfully"moved"disruptionsbythisstrategy.NotethatthisstrategydoesnotmovethealleleasalacZ-fusion.yIP5canbeusedifthisisrequired.
Antibioticsused:
Kanamycin,Kan(SigmaK800) | 10mg/mlinwater.Useat40ug/ml(Kan40) |
Ampicillin,Amp(SigmaA9518) | 50mg/mlinwater.Useat50ug/ml(Amp50) |