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1、tRNASynthesisandSecondaryarticleRegulationArticleContents.IntroductionTakuyaUeda,UniversityofTokyo,Tokyo,Japan.ProkaryoticSystemsKimitsunaWatanabe,UniversityofTokyo,Tokyo,Japan.EukaryoticSystems.SynthesisofMaturetRNA.SummaryTransferRNAisprimarilysynthesizedbyt
2、ranscriptionbyRNApolymeraseandbecomesthematureformviaseveralsteps:processing,splicing,CCAadditionandposttranscriptionalmodification.TheconcentrationofindividualtRNAmoleculesiscontrolledinordertomaintaincellularfunctions.Introductioneukaryotes,chloroplasts,plan
3、tmitochondriaandinsomebacteria,arealsosplicedoutbyaspecificendonucleaseandThesizeandcompositionoftheintracellulartransferRNAtheresultanttwoRNAfragmentsarejoinedbyRNA(tRNA)poolisregulatedatseveralstagesofRNAligase.TheCCAsequences,whicharecompletelycon-synthesisa
4、nddegradationtoensureefficienttranslationservedat3’terminiofalltRNAsknownsofar,arenotbytRNAmolecules.CodonsresidinginthereadingframesencodedintRNAgenesinsomespeciesandareofproteingenesencodedonthegenomesofindividualposttranscriptionallyaddedbyaCCA-addingenzyme.l
5、ivingorganismsarenotequallyutilized.SuchcodonAllmaturetRNAmoleculescontainmodifiednucleotidesbiasesmayreflectnucleotideselectionsresultingfromwhichareconsideredtobeinvolvedinthestabilizationofdirectionalmutationpressureduringevolution.Forstructureandindecodingpr
6、operties.Thesemodifiedexample,agenomewithahighGCcontentpreferentiallynucleotidesareconvertedfromcanonicalnucleotidesbycontainscodonscomprisingGorCinitsreadingframes.specificenzymesaftertranscriptionofprecursormole-CorrelationbetweencodonpreferenceandtheGCcontent
7、cules.ofagenomeisfoundmainlyinhighlyexpressedproteingenes;suchacorrelationdoesnotgenerallyholdforgenesexpressedatlowerlevels.Intheproteingenes,theconcentrationsoftRNAspeciesincellsarecloselyrelatedProkaryoticSystemstocodonbias.Forexample,inMicrococcusluteuswho
8、segenomicGCcontentisabout75%,correlationbetweenGene-dosageeffectscodonusageandthecontentofthecorrespondingtRNAspeciesisclearlyevident(Figure1).OnthebasisoftheAllthetRNAgenesontheEs
