Presentation is loading. Please wait.

Presentation is loading. Please wait.

Meccanismi di Regolazione dellespressione genica Fase Nucleare Scelta del gene che deve essere espresso Maturazione dellRNA Trasferimento Nucleo Citoplasma.

Similar presentations


Presentation on theme: "Meccanismi di Regolazione dellespressione genica Fase Nucleare Scelta del gene che deve essere espresso Maturazione dellRNA Trasferimento Nucleo Citoplasma."— Presentation transcript:

1

2 Meccanismi di Regolazione dellespressione genica Fase Nucleare Scelta del gene che deve essere espresso Maturazione dellRNA Trasferimento Nucleo Citoplasma Fase Citoplasmatica Sintesi delle catene polipeptidiche Modificazioni post-traduzionali Trasferimento delle proteine nelle sedi di competenza

3

4 Unione di ribonucleotidi monofosfato per formare una catena polinucleotidica I precursori della sintesi sono i nucleotidi trifosfato. Lenergia che occorre per la formazione del legame fosfodiesterico è data dalleliminazione del pirofosfato per idrolisi del legame.

5 ATP ADP ATP = Adenosin Trifosfato ADP = Adenosin Difosfato

6

7 ribosomal RNA (rRNA) 16S (small ribosomal subunit) 23S (large ribosomal subunit) 5S (large ribosomal subunit) transfer RNA (tRNA) messenger RNA (mRNA) Structure of prokaryotic messenger RNA 5 3 PuPuPuPuPuPuPuPuAUG Shine-Dalgarno sequenceinitiation The Shine-Dalgarno (SD) sequence base-pairs with a pyrimidine-rich sequence in 16S rRNA to facilitate the initiation of protein synthesis Classes of prokaryotic RNA AAU termination translated region

8 Classes of eukaryotic cellular RNAs ribosomal RNA (rRNA) 18S (small subunit) 28S (large subunit) 5.8S (large subunit) 5S (large subunit) transfer RNA (tRNA) messenger RNA (mRNA) heterogeneous nuclear RNA (hnRNA) (precursors of mRNA) small nuclear RNA (snRNA) U1, U2, U3, U4, U5, U6, U7, U8, U9, U10... small cytoplasmic RNA (scRNA) 7SL RNA What are the enzymes responsible for the synthesis of these RNAs?

9 The human RNA polymerases PolymeraseLocationProduct RNA polymerase I nucleolus 18S, 28S, 5.8S rRNA RNA polymerase II nucleoplasm hnRNA/mRNA, U1, U2, U4, U5 snRNA RNA polymerase III nucleoplasm tRNA, 5S RNA, U6 snRNA, 7SL RNA mitochondrial RNA polymerase mitochondrion all mitochondrial RNA _____________________________________________________________________________________________ Sensitivity of the nuclear RNA polymerases to -amanitin 1 RNA pol Iresistant RNA pol IIhigh sensitivity (binds with K = M) RNA pol IIIlow sensitivity (binds with K = M) 1 cyclic octapeptide from the poisonous mushroom Amanita phalloides

10 Structure of eukaryotic mRNA 7mGppp Cap 5 5 untranslated region AUG initiation translated region (A) ~200 poly(A) tail 3 untranslated region UGA termination 3AAUAAA polyadenylation signal all mRNAs have a 5 cap and all mRNAs (with the exception of the histone mRNAs) contain a poly(A) tail the 5 cap and 3 poly(A) tail prevent mRNA degradation loss of the cap and poly(A) tail results in mRNA degradation

11

12

13

14 53 promoter region exons (filled and unfilled boxed regions) introns (between exons) transcribed region translated region mRNA structure +1 b). Gene structure

15 Legame al promotore della RNA polimerasi Apertura della doppia elica Inizio della sintesi Allungamento Terminazione

16 Transcription RNA polymerase closed promoter complex open promoter complex initiation elongation termination RNA product

17 Direzione della sintesi Filamento senso Filamento antisenso

18

19 Sequence elements within a typical eukaryotic gene 1 GCTATACAATGC based on the thymidine kinase gene octamer transcription element promoter TATA box (TATAAAA) located approximately bp upstream of the +1 start site determines the exact start site (not in all promoters) binds the TATA binding protein (TBP) which is a subunit of TFIID GC box (CCGCCC) binds Sp1 (Specificity factor 1) CAAT box (GGCCAATCT) binds CTF (CAAT box transcription factor) Octamer (ATTTGCAT) binds OTF (Octamer transcription factor) +1 ATTTGCAT

20 Proteins regulating eukaryotic mRNA synthesis General transcription factors TFIID (a multisubunit protein) binds to the TATA box to begin the assembly of the transcription apparatus the TATA binding protein (TBP) directly binds the TATA box TBP associated factors (TAFs) bind to TBP TFIIA, TFIIB, TFIIE, TFIIF, TFIIH 1, TFIIJ assemble with TFIID RNA polymerase II binds the promoter region via the TFIIs Transcription factors binding to other promoter elements and transcription elements interact with proteins at the promoter and further stabilize (or inhibit) formation of a functional preinitiation complex 1 TFIIH is also involved in phosphorylation of RNA polymerase II, DNA repair (Cockayne syndrome mutations), and cell cycle regulation

21 NomeAliasChromosoma TAF1250Xq13.1 TAF1L250like9p21.1 TAF21508q24.12 TAF314010p15.1 TAF413520q13.33 TAF4B10518q11.2 TAF510010q24-10q25.2 TAF6807q22.1 TAF6L11q12.3 TAF7555q31 TAF7L50Xq22.1 TAF8436p21.1 TAF9325q11.2-5q13.1 TAF103011p15.3 TAF11286p21.31 TAF p35.3 TAF13181p13.3 TAF156817q11.1-q11.2 TF2D TBP + TAF

22 GTF 2

23

24 +1 TBP TFIID A B E F H J -25 TAFs Binding of the general transcription factors TFIID (a multisubunit protein) binds to the TATA box to begin the assembly of the transcription apparatus the TATA binding protein (TBP) directly binds the TATA box TBP associated factors (TAFs) bind to TBP TFIIA, TFIIB, TFIIE, TFIIF, TFIIH, TFIIJ assemble with TFIID

25 RNA pol II TBP TFIID A B E F H J RNA polymerase II (a multisubunit protein) binds to the promoter region by interacting with the TFIIs TFs recruit histone acetylase to the promoter Binding of RNA polymerase II

26

27 Steps in mRNA processing (hnRNA is the precursor of mRNA) capping (occurs co-transcriptionally) cleavage and polyadenylation (forms the 3 end) splicing (occurs in the nucleus prior to transport) exon 1 intron 1 exon 2 cap poly(A) cappoly(A) Transcription of pre-mRNA and capping at the 5 end Cleavage of the 3 end and polyadenylation Splicing to remove intron sequences Transport of mature mRNA to the cytoplasm

28 Polyadenylation cleavage of the primary transcript occurs approximately nucleotides 3-ward of the AAUAAA consensus site polyadenylation catalyzed by poly(A) polymerase approximately 200 adenylate residues are added poly(A) is associated with poly(A) binding protein (PBP) function of poly(A) tail is to stabilize mRNA mGpppNmpNm AAUAAA mGpppNmpNm AAUAAA A A A A A A 3 cleavage polyadenylation

29

30 Splicing Rimozione di un introne attraverso due reazioni sequenziali di trasferimento di fosfato, note come transesterificazioni. Queste uniscono due esoni rimuovendo lintrone come un cappio

31

32

33

34 GENE PREDICTION GeneScanGrailEXPPromoter 2.0 Omiga 2.0GeneMarkF GENE SH

35

36

37

38 Recognition of splice sites invariant GU and AG dinucleotides at intron ends donor (upstream) and acceptor (downstream) splice sites are within conserved consensus sequences small nuclear RNA (snRNA) U1 recognizes the donor splice site sequence (base-pairing interaction) U2 snRNA binds to the branch site (base-pairing interaction) Y= U or C for pyrimidine; N= any nucleotide G/GUAAGU …A …YYYYYNYAG/G donor (5) splice siteacceptor (3) splice sitebranch site U1 U2

39 Chemistry of mRNA splicing two cleavage-ligation reactions transesterification reactions - exchange of one phosphodiester bond for another - not catalyzed by traditional enzymes branch site adenosine forms 2, 5 phosphodiester bond with guanosine at 5 end of intron G-p-G-U A-G-p-G 2OH-A -53 intron 1 exon 1exon 2 Pre-mRNA First clevage-ligation (transesterification) reaction branch site adenosine

40 G-p-G-U A-G-p-G 2OH-A -53 intron 1 exon 1exon 2 Step 2: binding of U4, U5, U6 U1 U5 U2 U4 U6 G-p-G-U A-G-p-G 2OH-A -53 intron 1 exon 1exon 2 Step 3: U1 is released, then U4 is released U5 U2 U6

41 G-p-G53 U-G-5-p-2-AA 3 G-A intron 1 mRNA 2OH-A U5 U2 U6 Step 4: U6 binds the 5 splice site and the two splicing reactions occur, catalyzed by U2 and U6 snRNPs

42 G-OH 3 A-G-p-G U-G-5-p-2-A 53A A O - G-p-G53 U-G-5-p-2-AA 3 G-A Splicing intermediate Lariat exon 1 exon 2 intron 1 Second clevage-ligation reaction Spliced mRNA ligation of exons releases lariat RNA (intron)

43

44 Trans-splicing Nei protozoi e in un nematode

45

46

47

48

49

50 Differenti molecole di mRNA dallo stesso gene Splicing alternativo Uso di promotori alternativi Uso di segnali di poliadenilazione alternativi

51

52

53

54

55 Nei geni degli eucarioti gli enhancers possono distare dalla regione codificante anche più di 50 Kb. Enhancers

56

57

58


Download ppt "Meccanismi di Regolazione dellespressione genica Fase Nucleare Scelta del gene che deve essere espresso Maturazione dellRNA Trasferimento Nucleo Citoplasma."

Similar presentations


Ads by Google