Sinh học - Chapter 21 (part 1) Transcription

Chapter 21 (part 1)TranscriptionCentral DogmaRNA Content of E. coli CellstypeSteady State LevelsSynthetic CapacityStabilityrRNA83%58%HightRNA14%10%HighmRNA3%32%Very LowE. Coli RNA PolymeraseRNA polymerase core enzyme is a multimeric protein a2,b, b’, wThe b’ subunit is involved in DNA bindingThe b subunit contains the polymerase active siteThe a subunit acts as scaffold on which the other subunits assemble.Also requires s-factor for initiation –forms holo enzyme complexSite of DNA binding and RNA polymerizationGeneral Gene Structure5’3’Transcribed regionterminatorPromoterGene PromotersOther s-FactorsStandard genes – s70Nitrogen regulated genes – s54Heat shock regulated genes – s32Transcriptional InitiationClosed complexOpen complexPrimer formationDisassociation of s-factorPausing induces termination3’end tends to be AU rich easily to disrupt during pausing. Leads to disassembly of RNA polymerase complexRho Dependent Terminationrho is an ATP-dependent helicase it moves along RNA transcript, finds the "bubble", unwinds it and releases RNA chain Eukaryotic RNA PolymerasestypeLocationProductsRNA polymerase INucleolusrRNARNA polymerase IINucleoplasmmRNARNA polymerase IIINucleoplasmrRNA, tRNA, othersMitochondrial RNA polymeraseMitochondriaMitochondrial gene transcriptsChloroplast RNA polymerase ChloroplastChloroplast gene transcriptsEukaryotic RNA PolymerasesRNA polymerase I, II, and IIIAll 3 are big, multimeric proteins (500-700 kD) All have 2 large subunits with sequences similar to  and ' in E.coli RNA polymerase, so catalytic site may be conserved Eukaryotic Gene PromotersContain AT rich concensus sequence located –19 to –27 bp from transcription start (TATA box)Site where RNA polymerase II bindsTranscription FactorsTFAIIA, TFAIIB – components of RNA polymerase II holo-enzyme complexTFIID – Initiation factor, contains TATA binding protein (TBP) subunit. TATA box recognition. TFIIF – (RAP30/74) decrease affinity to non-promoter DNA