RNA synthesis in avian erythroid cells☆

[摘要] Innucleatederythroidcells,asinothervertebratecells,lessthan2%ofthenewlymadeRNAentersthecytoplasm.Posttranscriptionalselectionisthereforelikelytoplayanimportantroleindifferentialgeneexpression.Theworkreportedheredefinestherelativerolesoftranscription,nuclear-cytoplasmicflow,andmRNAturnoverindeterminingthedistanceofpolysomalmRNAsinavianerythroidcells.CellswerepreincubatedwithglucosaminetoreduceendogenouspoolsofUTPandwerethenlabeledwith[3H]uridine.ThespecificactivityoftheUTPpoolsduringtheincubationwasmeasuredafterhigh-pressureliquidchromatography,andtheabsoluteratesofsynthesisofnuclearandcytoplasmicRNAweredetermined.Underthelabelingconditionsdescribed,theUTPpoolreachedaspecificactivityof600dpm/pmolewithin5minandremainedbetween600and800dpm/pmolefor60min.ThetotalrateRNAsynthesiswas0.9fg/min/cell.TherateofsynthesisofcytoplasmicRNAwas1.7%ofthetotal.ComparisonofthesefigureswithpublisheddataforLcellsindicatesthattheseterminallydifferentiated,postmitoticcellsaremuchmorerestrictedintranscriptionthanLcells,butsimilarintheefficiencyofconvertingnucleartranscriptstocytoplasmicRNA.TherateofappearanceandsizedistributionofpolysomalRNAswerealsodetermined.About45%ofthenewlysynthesizedpoly(A)+polysomalRNAhasasedimentationcoefficientofapproximately9SandwasidentifiedasglobinmRNAbyhybridizationtorecombinantplasmidDNAcontainingchickenβ-globinmRNAsequence.EachspeciesofglobinmRNAiscalculatedtoarriveonpolysomesatabout1moleculeperminutepercellandeachspeciesofnonglobulinmRNAatabout0.02moleculesperminutepercell.Thesedifferencesintheratesofappearancedonotsufficetoexplainthe200-folddifferenceintheconcentrationsofindividualglobinandnonglobinpoly(A)+mRNAspeciesdeterminedinhybridizationexperiments.Thenonglobinpoly(A)+mRNAsinthesecellsmustthereforeeitherbelessstablethantheglobinmRNAorhaveaccumulatedforashortertimethantheglobinmRNA.

[学科分类] 生物科学（综合）