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.
9I geni per gli rRNA sono ripetuti in tandem nei genomi eucariotici ETS18SITS28SNTSRNARNADNADNAgenepromoter60/81 bprepeatsspacerother repetitiveelementsDNA
10I precursori degli rRNA sono piu' lunghi della somma degli rRNA maturi
11rRNA 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.
13Il complesso d'inizio della pol I The structural organization of mammalian rDNA repeats and the basal factors required for transcription initiation. The diagram showsthe arrangement of tandemly repeated rRNA genes. The site of transcription initiation of 47S pre-rRNA (black arrow) and intergenictranscripts from the spacer promoter (red arrow) are indicated. Terminator elements are located downstream of the transcription unit(T1−10), downstream of the spacer promoter (TSP), and upstream of the gene promoter (To) (red boxes). Repetitive enhancer elements(gray boxes) are located between the spacer promoter and major gene promoter. The ellipsoids show the factors that are associated withthe rDNA promoter and Pol I, respectively. TTF-I is associated with the upstream terminator To. Synergistic binding of UBF andTIF-IB/SL1 to the rDNA promoter is required for the recruitment of RNA polymerase I (Pol I)—together with multiple PolI-associated factors—to the transcription start site to initiate pre-rRNA synthesis.
14Il complesso d'inizio della pol I UBF: inizio, allungamentoSL1: inizioTIF-1A (RRN3): inizioTTF-1: terminazione
15Regolazione della sintesi dell'rRNA Regulation of Pol I transcription in response to external signals. The bar diagrams show the relative levels ofpre-rRNA upon exposure of cells to amino acid starvation (left), exposure to oxidative stress (middle), andgrowth factor stimulation (right).
16Regolazione della sintesi dell'rRNA Regulation of Pol I transcription during cell cycle progression. UBF is activated during interphase byphosphorylation of serine 484 (S484) by Cdk4/cyclin D and phosphorylation of serine 388 (S388) byCdk2/cyclin E and A. At the entry into mitosis, phosphorylation of TAFI110 at threonine 852 (T852) byCdk1/cyclin B inactivates TIF-IB/SL1. At the exit from mitosis, Cdc14B dephosphorylates T852, leading torecovery of TIF-IB/SL1 activity. Activating phosphorylations are marked in green, inhibiting ones in red.
24Esempi di box del tipo “elemento di risposta” AgenteregolatoreModuloConsensusFattoreGrandezza(dalton)Shock termicoGlucocorticoidiCadmioTPASieroHSEGREMRETRESRECNNGCCNNTCCNNGTGGTACAAATGTTCTCGNCCCGGNCNCTGACTCACCATATTAGGHSTFRecettore?AP1SRF93,00094,00039,00052,000
40LCR 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.