In1955FrancisCrickhypothesizedthattherewereintermediatemoleculeswhichparticipatedintrans-ferringgeneticinformationfromDNAtoprotein.TheintermediatemoleculewasRNA.In1958heputforththefamouscentraldogma.-----DNA--------RNA------protein--------Temin1970In1961theDNAdependentRNApolymerasewasdiscoveredinEcoliandthestudyonthemechanismoftranscriptionbegan.In1982ThomasCechdiscoveredthatoneoftheprecursorRNAinTetrahymenachouldactasacatalystandcatalyzedself-splicing.Itisaribozyme.Section1DNAdependentRNAsynthesisRNAsynthesisiscatalyzedbyDDRP(orsimplyRNApolymerase.)CharacteristicsofRNAsynthesisTemplateDNA(onestrandDNAindsDNA,templatestrand)SubstratefourkindsofNTPEnzymeDDRP(noreqirementofprimer,noproof-readingfunction)DirectionofRNAchain5’to3’synthesisBasepairingGCTAAUruleInorganicMg++Zn++ionTheprocessoftranscriptioncanbedividedintothreestages:initiation,elongationandtermination.seethefig.ontheblackboardThetwostrandsindsDNAarecomplementary.Theyarethecodingstrandandthetemplatestrand.ThetemplatestrandworksasthetemplateforthesynthesisofRNA.ThesynthesizedRNAiscomplementarytothetemplatestrand.ItssequenceisthesameasthatofthecodingstrandwiththeexceptionofthesubstitutionofUforT.RNApolymeraseThereisonlyonetypeofRNApolinprokaryoteswhiletherearethreetypesofRNApolsineukaryotes.EcoliRNApolymeraseEcoliRNApolcatalyzessynthesisofalltheRNAs(mRNA,rRNA,tRNAetc)StructureofEcoliRNApolymeraseTheholoenzymeofEcoliRNApolcontainsα2ββ’(ω)σsubunitsTheσsubunitcanbedissociatedfromtheholoenzyme.TheRNApolwithoutσsubunitiscalledcoreenzyme:α2ββ’(ω)FunctionoftheSubunitσcanrecognizepromotersandinitiatetranscription.αcanbindregulatoryproteinsandcontrolthetranscriptional.rate.β+β’catalyzesRNAsynthesis.Theremaybeωsubunit.Itsfunctionisunknown.Therearedifferentkindsofσsubunits.Themostcommononeisσ70.EukaryoticRNApolymerasesRNApolIRNApolIIRNApolIII____________________________________________________Product45SrRNAhnRNAtRNAsynthe