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CONTRÔLE
DE
L’EXPRESSIONDESGENES
DeniseAragnol
Instabilitédugénomeetcancérogenèse
CNRS/UniversitédelaMéditerranée
Chezleseucaryotes
DEFINITION D’EXPRESSION GENIQUE
Expression génique : recouvre l’ensemble des mécanismes quiconduisent à l’apparition d’un produit fonctionnel d’un gène
Produit fonctionnel:
-Une protéine transcription + traduction
-Un ARN transcription
LES DIFFERENTS TYPES D’ARN
traduction
CELLULES DIFFERENCIEES DE MAMMIFERES
Elles possèdent le même génome mais n’expriment pas les mêmes gènes
nucleus
cytoplasm
a more accurate outline of the events involved ingenome expression, especially in higher organisms.Note that these schemes apply only to protein-codinggenes. Those genes that give rise to non-coding RNAsare transcribed and processed as shown but the RNAsare not translated.
TOUTES LESETAPES DE
L’EXPRESSIONGENIQUE SONT
REGULEES
RNA localisation
Protein localisation
UN EXEMPLE D’ARNm LOCALISE
Movement of RNA-containing granules in dendrites of cultured neurons. a–k |Time-lapse images, taken 20 s apart, of an anterograde-moving granule (arrow). Thegranule is detected by visualization of fluorescent SYTO-14, which binds to RNA. Thegranule moves more than 5 m, with an average velocity of 0.04 m s-1. Thismovement was stimulated by depolarization
IMPORTANCE DES INTERACTIONS MOLECULAIRES
nucleus
cytoplasm
TOUTES LESETAPES DE
L’EXPRESSIONGENIQUE SONT
REGULEESRNA localisation
Protein localisation
UN SYNOPSIS DE LA TRANSCRIPTION
LES PROMOTEURS EUCARYOTES SONTCOMPLEXES
EXEMPLE DE PROMOTEUR RECONNU PAR L’ARN POL II
Eukaryotic promoters consist ofa collection of conserved shortsequence elements located atrelatively diverse distances fromthe transcription start site.
Alternative orientations for GC and CAAT box elements are indicated by chevron orientation: > =normal orientation; < = reverse orientation. The glucocorticoid receptor gene is unusual inpossessing 13 upstream GC boxes (10 in the normal orientation; three in the reverse orientation).
L’ORGANISATION DES PROMOTEURSEUCARYOTES EST DIFFERENTE D’UN GENE A UN
AUTRE
LES ARN POLYMERASES EUCARYOTES-3 ARNpol différentes: ARN pol I, ARN Pol II, ARN Pol III compositions et
fonctions différentes, structures similaires
-multimériques (8 à 12 s. u.); >500kDa; L’ARNpol II eucaryote est constituée deplus de 10 sous-unités
Functions of the three eukaryotic nuclear RNA polymerases
Polymerase Genes transcribed____________________________________________________
RNA polymerase I (nucléole) 28S, 5.8S and 18S ribosomal RNA (rRNA) genes
RNA polymerase II Protein-coding genes; mostsmall nuclear RNA (snRNA)genes
RNA polymerase III Genes for transfer RNAs (tRNA), 5S rRNA, U6-snRNA,small nucleolar (sno) RNAs,small cytoplasmic (sc) RNA
STRUCTURE DE L’ARN pol II (2001)
Structure cristallographiquede l ’ARN polymérase II.A. Enzyme libre à unerésolution de 2,8 Å.L ’enzymecontient un sillon (Rpb1)bordéà son entrée par une paire demâchoires, supérieure (partiede Rpb1 et Rpb9) et inférieure(Rbp5), et au fond duquel setrouvent deux ions Mg 2+ quiindiquent l ’emplacement dusite actif. Près du site actif,l’hélice de pontage (Rpb1)traverse le sillon pour rejoindreRpb2. Le pore localisé à l’arrière de l ’enzymepermettrait l’entrée des rNTP etla sortie de l ’extrémité 3 ’ libre(Protein Data Bank AccessionCode :1i50).
B.Enzyme en élongation àune résolution de 3,3 Å.Lapince formée de parties deRbp1 et Rbp2 effectue unerotation de 30 ° qui maintientla matrice d ’ADN et letranscrit au sein du complexetranscriptionnel. L’extrapolation du trajetprobable des acidesnucléiques au sein de l’enzyme montre que l ’ADNdouble brin situé en aval faitcontact avec la mâchoireinférieure puis passe entre lelobe de Rbp2 et une partie dela pince formée parRbp1.Des flèches indiquentles sites d ’entrée et de sortiede l ’ADN (Protein Data BankAccession Code :1i6H).Violet :mâchoiresupérieure;rose :mâchoireinférieure;jaune :lobe;vertfoncé :sillon;blanc :hélice depontage;orange :site actif;vertpâle : pore;bleu :mur;rouge:pince;bleu pâle :ions Mg2+(Protein Data BankAccession Code :1i50).Bleu:brin matrice;vert :brincodant;rose :ARN. Le codede couleur des domaines de l’enzyme est le même qu ’en(A)
LES CARACTERISTIQUES DU DOMAINE C-TER del’ARN pol II
La RNA pol II possède un domaine C terminal particulier, constitué de répétitions d’unheptapeptide (tyr-ser-pro-thr-ser-pro-ser) qui peut présenter différents niveaux dephosphorylation
LES FACTEURS GENERAUX
PIC: préinitiationcomplex
TAACCAAT TATA
ATAT
TAACCAAT TATA
ATAT
5’
5’
5’
5’
3’
3’3’
3’
5’
5’
DEBUT DE L’ELONGATION
ELONGATION ET MATURATION SONT COUPLEES
ADDITION DE LA COIFFE
The C-Terminal Domain (CTD) of RNA Polymerase II Coordinates Transcription and Pre-mRNA ProcessingThe CTD consists of 52 repeats of the consensus heptapeptide Tyr-Ser-Pro-Thr-Ser-Pro-Ser and serves as a platform for the ordered assembly of the factorsresponsible for transcription, pre-mRNA 5′ capping, splicing, and 3′ processing at differentstages in the synthesis of the nascent transcript.
Structure of U1-snRNP. The mammalianU1-snRNP comprises the 165-nucleotideU1-RNA plus ten proteins. Three of these(U1-70K, U1-A and U1-C) are specific tothis snRNP, the other seven are Smproteins that are found in all the snRNPsinvolved in splicing. The U1-RNA forms abase-paired structure as shown. The U1-70K and U1-A proteins attach to two of themajor stem-loops of this base-pairedstructure, and U1-C attaches via a protein-protein interaction. The Sm proteins attachto the Sm site. Based on Stark et al. (2001)
L’EXCISIONEPISSAGE DESINTRONS
CPSF: Cleavage &polyadenylationspecificity factor
CstF: cleavage stimulation factor
PAP: polyA polymerase
FORMATION DE L’EXTREMITE 3’ DE L’ARNm
DE NOUVELLES INTERACTIONS AU NIVEAU DUCTD DE L’ARN pol II
Schematic representation of thepolyadenylation machinery. The majority ofthe components of the mammalian andyeast polyadenylation complexes areconserved, including all currently knownfactors that function in the transcriptionconnection. For simplicity, only themammalian nomenclature is depicted; theyeast names of factors that have importantroles in the events described here are alsoindicated. (Note that although an apparenthuman homolog of Ssu72 exists, it has notyet been characterized functionally). ,documented protein–protein interactionsthat help link transcription and 3'processing (see text). Polyadenylationsignal sequences (upstream AAUAAA, CAcleavage site consensus, and downstreamG/U-rich region) are boxed. CPSF,cleavage-polyadenylation specificity factor;CstF, cleavage stimulation factor; CFI andCFII, cleavage factors I and II, respectively;PAP, poly(A) polymerase.
cytoplasme
noyau
cytoplasme
noyau
LA TRANSCRIPTION EST REGULEE
DES FACTEURS DE TRANSCRIPTION SPECIFIQUESINTERAGISSENT AVEC LA MACHINERIE BASALE
DE TRANSCRIPTION
ACTIVATION TRANSCRIPTIONNELLE PAR UNEHORMONE
CHROMATINE ET TRANSCRIPTION
LA CHROMATINE
C’est la structure macromoléculaire ADN-protéine présente dans le noyau des celluleseucaryotes
Le nucléosome
147 pb d’ADN sont enroulésautour de l’octamere d’histone,formant deux tours
LA CHROMATINE CONSTITUE UN CONTEXTETRANSCRIPTIONNEL REPRESSIF
Histone Modifications on the Nucleosome Core ParticleThe nucleosome core particle showing 6 of the 8 core histone N-terminal tail domains and 2 C-terminal tails. Sites of posttranslational modification are indicated by coloredsymbols that are defined in the key (lower left); acK, acetyl lysine; meR, methyl arginine; meK, methyl lysine; PS, phosphoryl serine; and uK, ubiquitinated lysine. Residuenumbers are shown for each modification. Note that H3 lysine 9 can be either acetylated or methylated. The C-terminal tail domains of one H2A molecule and one H2Bmolecule are shown (dashed lines) with sites of ubiquitination at H2A lysine 119 (most common in mammals) and H2B lysine 123 (most common in yeast). Modifications areshown on only one of the two copies of histones H3 and H4 and only one tail is shown for H2A and H2B. Sites marked by green arrows are susceptible to cutting by trypsin inintact nucleosomes. Note that the cartoon is a compendium of data from various organisms, some of which may lack particular modifications (e.g., there is no H3meK9 in S.cerevisiae). Adapted from Spotswood and Turner (2002 ).
LE CODE HISTONE
REGULATION DE LA TRANSCRIPTION DU GENEIFN-β
L’EPIGENETIQUE
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