Figure 2 | 3'–5' interactions: circles of mRNA

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1 Figure 2 | 3'–5' interactions: circles of mRNA
Figure 2 | 3'–5' interactions: circles of mRNA.   a | Visualization of circular RNA–protein complexes by atomic-force microscopy. Complexes formed on capped, polyadenylated double-stranded RNA in the presence of eIF4G, poly(A)-binding protein (PABP) and eIF4E91. (Picture provided by A. Sachs and reprinted with permission.) b | Model of messenger-RNA circularization and translational activation by PABP–eIF4G–eIF4E interactions. eIF4G simultaneously binds to eIF4E and PABP7, 9, 14, 53, 55, thereby circularizing the mRNA91 and mediating the synergistic stimulatory effect on translation of the cap and poly(A) tail by enhancing the formation of the 48S complex53, 54, 92. c | Model of mRNA circularization and translational activation by PABP–Paip1 interactions. Paip1 is a PABP-interacting protein that binds eIF4A93, acting as a translational co-activator. d | Model of mRNA circularization and translational repression by CPEB–maskin–eIF4E interactions. RNA-associated CPEB binds maskin, which in turn binds to the eIF4E. This configuration of factors precludes the binding of eIF4G to eIF4E and thus inhibits assembly of the 48S complex13. e | Model of translational repression by heterogeneous nuclear ribonucleoproteins (hnRNPs). The differentiation control element (DICE), located in the 3' UTR of 15-lipoxygenase mRNA, inhibits translation initiation by preventing the joining of the 60S ribosomal subunit to the 43S complex located at the AUG codon. This inhibition is mediated by hnRNP proteins K and E1. The inhibitory event probably targets one of the initiation factors involved in the GTP hydrolysis that releases the initiation factors and the joining of the 60S ribosomal subunit2, 94. ORF, open reading frame.

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7 Ruolo di PABP nella traduzione
In estratti “cell free” di lievito sinergismo tra cap e coda poli(A) Interazione tra PABP e eIF4G eIF4E, eIF4G, PABP e mRNA forma strutture circolari (in vitro) Altre proteine che interagiscono con PABP (Paip1, 2 e eRF3)

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9 Initiation Factor Activity
eIF Fidelity of AUG codon recognition eIF-1A Facilitate Met-tRNAiMet binding to small subunit eIF Ternary complex formation eIF-2B (GEF) GTP/GDP exchange during eIF-2 recycling eIF-3 (10 subunits) Ribosome subunit antiassociation, binding to 40S subunit eIF-4F (4E, 4A, 4G) mRNA binding to 40S, ATPase-dependent RNA helicase activity eIF-4A ATPase-dependent RNA helicase eIF-4E 5' cap recognition eIF-4G Scaffold for of eIF-4E and -4A in the eIF-4F complex eIF-4B Stimulates helicase, binds simultaneously with eIF-4F eIF-4H              Similar to eIF4B    eIF Release of eIF-2 and eIF-3, ribosome-dependent GTPase eIF5B Subunit joining eIF Ribosome subunit antiassociation

10 Inizio di traduzione nell’mRNA di poliovirus
AUG AUG AUG AUG UUUCCUUUU A U G IRES= Internal ribosome entry site

11 Saggio dell’mRNA bicistronico
+++ +/- CAT luciferasi cap +++ CAT luciferasi cap IRES (+) +++ CAT luciferasi cap IRES (+/0) +++ CAT luciferasi cap IRES 4F

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14 Model for assembly of 48S complexes on EMCV-like IRESs
Model for assembly of 48S complexes on EMCV-like IRESs. Structural domains of the IRES and regions of contact with the following factors as determined by footprinting are shown: eIF4G/4A complex (blue/green), ITAF 45 (diamonds), PTB (gray). PTB contains four RRM domains and binds multiple sites on EMCV-like IRESs; such binding (indicated by a dotted line) therefore may stabilize a specific conformation of the IRES. The recruitment of a 40S ribosomal subunit (red) carrying initiator tRNA and eIF3 (yellow) is shown. See text for details.

15 eIF3 40S

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24 CARATTERISTICHE DI UN "SISTEMA VIVENTE"
® replicazione ® evoluzione

25 FUNZIONI DELL'RNA NELLA CELLULA MODERNA
® traduzione rRNA, mRNA, tRNA ® maturazione rRNA snoRNA, RNasi MRP ® splicing snRNA, introni gruppi I e II ® maturazione tRNA RNasi P ® sintesi DNA primers, telomerasi ® traslocaz. proteine srpRNA

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28 PERCHE' L'RNA? ® l'RNA deve essere venuto prima del DNA
l'RNA deve essere venuto prima delle proteine ® molti coenzimi hanno un ribonucleotide nella struttura l'RNA può agire come catalizzatore