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mRNA. Cap Poly(A) tail Secondary structures IRES uORF Protein/RNA binding sites AUG Kozak consensus sequence: GCC( A / G )CC AUG G. Fátima Gebauer & Matthias W. Hentze Nature Reviews Molecular Cell Biology 5, 827-835 (2004). Scanning model of Cap-dependent Translation Initiation. E.
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mRNA Cap Poly(A) tail Secondary structures IRES uORF Protein/RNA binding sites AUG Kozak consensus sequence: GCC(A/G)CCAUGG Fátima Gebauer & Matthias W. Hentze Nature Reviews Molecular Cell Biology 5, 827-835 (2004)
Scanning model of Cap-dependent Translation Initiation E P A eIF5B Fátima Gebauer & Matthias W. Hentze Nature Reviews Molecular Cell Biology 5, 827-835 (2004) E P A
http://departments.oxy.edu/biology/Stillman/bi221/091300/091300_lecture_figures.htmhttp://departments.oxy.edu/biology/Stillman/bi221/091300/091300_lecture_figures.htm
Scanning model of Cap-dependent Translation Initiation E P A eIF5B Fátima Gebauer & Matthias W. Hentze Nature Reviews Molecular Cell Biology 5, 827-835 (2004) E P A
Translation of mRNAs in ∆eIF5B Yeast { Polysomes { Actin Northern
Recycling of the ternary complex requires eIF2B Fátima Gebauer & Matthias W. Hentze Nature Reviews Molecular Cell Biology 5, 827-835 (2004)
eIF2 Phosphorylation Reduces Ternary Complex Starvation (GCN2) Viral infection, apoptisis (PKR) ER Stress (PERK) Haemin-regulated inhibitor (HRI) Fátima Gebauer & Matthias W. Hentze Nature Reviews Molecular Cell Biology 5, 827-835 (2004)
uORFS 1 2 3 4 GCN4
GCN4: Non-starvation Starvation
eIF4E binding proteins: 4E-BP Apoptosis Insulin AA (Leucine) Cell Proliferation
SJ Morley, MJ Codwell, MJ Clemens (2006) Cell Death and Diff. 12, 571-584.
IRE/IRP: steric hindrance IRE-IRBP Thomson et al. (1999) Intnl. J. Biochem & cell Biol. 31, pp 1139-1152.
Sex-lethal: SXL Ann-Bin Shyu. Nature Struct. & Molec. Biol. (2006) 13, 189-190.
Viral IRES X&Y=> IRES Trans-acting factors Stoneley and Willis (2004) Oncogene 23, 3200-3207
IRES Mechanisms of Internal Initiation IRES
Cap-Independent Translation Initiation • Cellular • Cellular stress: viral infection (PKR), apoptosis, hypoxia • Normal cellular processes: G2/M phase cell cycle • Viral • Genomes: Picornaviruses, Hepatitis C Virus, Cricket paralysis virus • Specific viral messages: HIV, Herpes virus (…. and the list is still growing!)
Cellular IRESes: How do they recruit 40S? • Widely assumed that the Secondary and tertiary Structure allow for interactions with translational machinery (ITAF,eIFs, 40S) • No common Structure • Composed of multiple short modules • Generally 150-300 nts long, exception: 9nt repeated element.
mRNA-rRNA base-pairing Dresios et al. (2006) Nature Struct.& Mol. Bio. 13, 30-34.
Summary • Mechanisms of initiation: • Cap-dependent translation • Cap-independent translation: Internal ribosome entry sites • Regulation of initiation: • Global • eIF2 alpha phosphorylation • 4E-BPs • Cleavage of eIF4G • Message specific • GCN4 • IRE/IRP • SXL • miRNA (microRNA)