4RNA polymerases RNA polymerase I synthesizes rRNA in the nucleolus. RNA polymerase II synthesizes mRNA in the nucleoplasm.RNA polymerase III synthesizes small RNAs in the nucleoplasm.All eukaryotic RNA polymerases have ~12 subunits and are aggregates of >500 kD.Some subunits are common to all three RNA polymerases.The largest subunit in RNA polymerase II has a CTD (carboxy- terminal domain) consisting of multiple repeats of an eptamer.
5I geni per gli rRNA sono ripetuti in tandem nei genomi eucariotici ETS18SITS28SNTSRNARNADNADNAgenepromoter60/81 bprepeatsspacerother repetitiveelementsDNA
6I PRECURSORI DEGLI rRNA SONO PIU' LUNGHI DELLA SOMMA DEI DUE rRNA MATURI
7rRNA genesRibosomal RNA is coded by a large number of identical genes that are tandemly repeated to form a cluster(s).Each rDNA cluster is organized so that transcription units giving a joint precursor to the major rRNAs alternate with nontranscribed spacers.
20ELEMENTI DI RISPOSTA Agente regolatore Modulo Consensus Fattore Grandezza(dalton)Shock termicoGlucocorticoidiCadmioTPASieroHSEGREMRETRESRECNNGCCNNTCCNNGTGGTACAAATGTTCTCGNCCCGGNCNCTGACTCACCATATTAGGHSTFRecettore?AP1SRF93,00094,00039,00052,000
21Response elementsResponse elements may be located in promoters or enhancers.Each response element is recognized by a specific transcription factor.A promoter may have many response elements, which may activate transcription independently or in certain combinations.
37LCR and insulatorsAn LCR is located at the 5 end of the domain and consists of several hypersensitive sites.Insulators are specialized chromatin structures that have hypersensitive sites.All known insulators are able to block passage of any activating or inactivating effects from enhancers, silencers, or LCRs.In some cases, insulators have directionality, and may stop passage of effects in one direction but not the other.
38Possono essere distinti in: - Fattori generali - Fattori a monte FATTORI DI TRASCRIZIONE NEGLI EUCARIOTI( trans-acting factors = fattori che agiscono in trans )Possono essere distinti in:- Fattori generali- Fattori a monte- Fattori inducibili
39Assemblaggio del complesso di inizio su un promotore Pol II Pol Pol II TATA-1-2-3-4-512TFII DTFII ATFII BPol IITFII E1 TBP +vari TAFTFIIF
42Le tre RNA polimerasi sono posizionate a livello di tutti i promotori da un fattore che contiene la TBP
43Initiation at pol II promoters Binding of TFIID to the TATA box is the first step in initiation.Other transcription factors bind to the complex in a defined order, extending the length of the protected region on DNA.When RNA polymerase II binds to the complex, it initiates transcription.
44Later events of pol II initiation TFIIE and TFIIH are required to melt DNA to allow polymerase movement.Phosphorylation of the CTD may be required for elongation to begin.Further phosphorylation of the CTD is required at some promoters to end abortive initiation.The CTD may coordinate processing of RNA with transcription.