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1、Vol451
2、24January2008Q&AMOLECULARBIOLOGYTheexpandingworldofsmallRNAsHelgeGroßhansandWitoldFilipowiczMolecularcellbiologyhaslongbeendominatedbyaprotein-centricview.Buttheemergenceofsmall,non-codingRNAschallengesthisperception.TheseplentifulRNAsregulategeneexpressionatdifferentlevels,andhavee
3、ssentialrolesinhealthanddisease.HowmanyclassesofRNAhaveforinactivationbyclassicalgenetictools.More-percentofprotein-codinggenes.Moreover,beenidentified?over,manymiRNAscancompensateforeachnewclassesofsmallRNAscontinuetobeTherearethreemaintypesof‘classic’RNA:other’sfunction,whichmakestheirid
4、entifica-discovered.messengerRNA,transferRNAandribosomaltiononthebasisoftheovertconsequencesofRNA.mRNAsaretranslatedintoproteins,theirabsencedifficult.ThefirsttwomiRNAsDoallorganismshavesmallRNAs?whereastRNAsandrRNAshavehousekeepingtobediscovered,lin-4andlet-7,wereidentifiedWiththenotablee
5、xceptionofthebuddingyeastrolesduringmRNAtranslation.SmallRNAsinthe1990sthroughgeneticexperimentsinSaccharomycescerevisiae,almostalleukaryo-arenottranslatedintoproteins.Instead,thesethewormCaenorhabditiselegans.ThensiRNAsticorganisms(thecellsofwhichcontaina20–30-nucleotidesequencesregulatev
6、ari-wereidentifiedinanimals,plantsandfungiasnucleus)investigatedsofarhavesiRNAsorousbiologicalprocesses,oftenbyinterferingtheeffectormoleculesthatmediatetheprocessatleastcellularmachineriestoproducethem.withmRNAtranslation.SmallRNAscomeinofsequence-specificgenesilencing,orRNAEvolutionarily
7、,miRNAsseemtobeyoungerdifferentforms(Box1),thebest-understoodinterference(RNAi),inresponsetodouble-thansiRNAs.miRNAsfunctionprimarilyclassesbeingsmallinterferingRNAs(siRNAs),strandedRNA(dsRNA;Fig.1).Thediscov-inmulticellularorganisms,althoughtheymicroRNAs(miRNAs)andPiwi-associatederyofRNAi
8、earneditstwoleadresearchers,haverecentlybeenidentifiedinaunicellularRNAs(piRNAs).AndrewFireandCraigMello,the2006Nobelalga,Chlamydomonasreinhardtii.CertainPrizeinPhysiologyorMedicine.DNAvirusesalsoexpressmiRNAs.AlthoughWhenweresmallRNAsdiscovered?20–30-nucleoti
