Class Notes (810,567)
Canada (494,151)
Biology (2,097)
BIO206H5 (179)
Lecture 9

BIO206 Lecture 9 Chapter 7.pdf

13 Pages
Unlock Document

University of Toronto Mississauga
George S Espie

Lecture 9/ Chapter 7 October-12-13 7:13 PM Eukaryotic transcription - More complicatedthan prokaryotic - Larger genome – more genes to recognizeand transcribe - RNA synthesis in the nucleus - DNA organization:tightly condensed chromatin with many proteins [bacterial DNA has far fewer proteins] Typical EukaryoticGene Termination site – trimming site where RNA molecule gets cut down Coding region (exons and introns)– exons containinformationthat will be translated Introns are interveningprocess that will be removed Eukaryotic hnRNA: Monocistronicmessage Primary transcript- Process that remove introns 3 Stagesof Transcription Initiation bindingof RNA polymeraseto a promoter sequence Elongation sequentialaddition of ribonucleotides as prescribed by the DNA templatestrand Termination dissociation of RNA polymerase (remove from DNA) release of primary transcript from template Initiation of eukaryoticgene transcriptionis a complex process - 3 RNA polymerase:RNA polymeraseI, RNA polymeraseII, RNA polymerase III ○ RNA polymerase I: transcribelarger rRNAs (28S, 18S, 5.8S) ○ RNA polymerase II: mRNAs, most small nuclearRNAs (snRNAs and snoRNAs), most microRNAs, and telomeraseRNA ○ RNA polymerase III: small RNAs, including tRNAs, 5S rRNA, and U6 snRNA ○ RNA polymerase IV, V (plantsonly): siRNAs (silencing genes) - Eukaryoticcell needs to generateso manyribosomes that transcription of rRNA occurs almost simultaneously - Require assistanceof accessory proteins.EX: generaltranscription factors - Mechanisms that control transcriptioninitiation is much more elaborate - Packingof DNA into nucleosomes and more compactforms of chromatinstructure - Larger genome-more genes to recognizeand transcribe Bacteria:500 - 6000 thousand genes Eukaryotes: tens of thousands of genes - Finding the transcription initiation site is difficult TranscriptionInitiation Complex: Overview EnhancersAnd Repressors • Other regions of DNA attractproteins which may enhance [increase] or repress [decrease] transcription • Also require transcriptional activators, mediators,chromatin& histone remodellingcomplexes Enhancer+ Initiation Complex Enhancer+ Initiation Complex Mediator complex– must take multiple (4-5) protein interactionin order for transcriptionto occur TranscriptionInitiation Site • Eukaryotic promoters • Generaltranscriptionfactors (GTFs) find & bind the promoter BEFORE pol II binds. Promoter - a specific sequenceof DNA involved in binding RNA polymerase and initiating transcription. - Contains the transcriptionstart site - “Oriented”sequencethat points RNA polymerase in one or the other direction on the DNA molecule - Once oriented polymerasesynthesizes RNA in 5' to 3' direction - Differentpromoters for differentpolymerases Class II Promoters Promoters recognized by RNA polymerase II (class II promoters)are similar to prokaryotic promoters Consideredto have two parts: - Core promoterhaving 4 elements  TATA box locatedat -25  BRE  INR  Downstreampromoterelement (DPE) is within 5’ UTR - Upstreampromoter element  UpstreamCAAT box Proximal PromoterConsensusSequences • CCAAT-box-bindingtranscription factor(CTF) Eukaryotic RNA Polymerase requiresgeneral transcriptionfactors- assembleson promoter - TATA box = promoterscontainthe TATA sequence ○ Typically located 25 nucleotidesupstreamfrom the transcription start site ○ Forms completetranscription initiation complex - TATA-bindingprotein (TBP) binds to TATA box sequencesand distorts DNA ○ Subunitof TFIID Consensussequence:The sequencethat reflects the most commonchoice of nucleic acid, or amino acid, at each positionwhen looking at a series of relatedDNA, RNA or protein sequences. Frequently, areas of agreementrepresent conserved functional motifs INR ConsensusSequence Py Py A N T/A Py PY Eukaryotic /Prokaryotic Proximal Promoter Inr Initiationsite for transcription TATA -35 to -20 TBP CAAT box & GC box -200 to -70 CAAT bindingprotein, BRE -35 TFIIB recognitionelement SSRCGCC DPE +35 downstreamcore promoter element RGWYV Abbreviations Letter Nucleotide(s)included Letter Nucleotide(s)included A A T T G G C C R G or A (Purine) Y T or C (Pyrimidine) M A or C K G or T S G or C W A or T H A or C or T B G or T or C V G or C or A D G or T or A N G or T or A or C Distal Promoters: GC and CAAT boxes Regulatory Regionsof EukaryoticGenes Inr Initiation site for transcription TATA -35 to -20 TBP TATA -35 to -20 TBP CAAT box & GC box -200 to -70 CAAT bindingprotein, BRE -35 TFIIB recognitionelement SSRCGCC DPE +35 downstreamcore promoter element RGWYV GC sp1 family W=T or A Y= pyrimidine S= C or G R = purine V=AGC (not a T) In vivo and in vitro experimentsprove that they are general binding factors Enhancers& Repressors Other regions of DNA attractproteins which may enhance [increase] transcription or repress [decrease] transcription Also require: • transcriptionalactivators • mediators • chromatin remodelingcomplexes • histone remodelingcomplexes TranscriptionInitiation Complex Eubacteria: Core RNA polymeraserequires σ factor to recognize -10 & -35 regions of the promoter Eukaryotes: Core RNA polymeraseII also requires ‘help’ to recognize the promoter: TFIID (TBP, TAF), TFIIA and TFIIB Generaltranscriptionfactors (GTFs) are proteins requiredto recognize promoter and bind RNA polymeraseII polymeraseII Formationof Preinitiation Complex • TFIID with help from TFIIA binds to the TATA box formingthe DA complex • TFIIB binds next generatingthe DAB complex • TFIIF helps RNA polymerasebind to a region from -34 to +17, now it is DABPolF complex • Last the TFIIE then TFIIH bind to form the completepreinitia
More Less

Related notes for BIO206H5

Log In


Don't have an account?

Join OneClass

Access over 10 million pages of study
documents for 1.3 million courses.

Sign up

Join to view


By registering, I agree to the Terms and Privacy Policies
Already have an account?
Just a few more details

So we can recommend you notes for your school.

Reset Password

Please enter below the email address you registered with and we will send you a link to reset your password.

Add your courses

Get notes from the top students in your class.