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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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slide1

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)

slide2

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

slide3

http://departments.oxy.edu/biology/Stillman/bi221/091300/091300_lecture_figures.htmhttp://departments.oxy.edu/biology/Stillman/bi221/091300/091300_lecture_figures.htm

slide4

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

slide7

Recycling of the ternary complex requires eIF2B

Fátima Gebauer & Matthias W. Hentze

Nature Reviews Molecular Cell Biology

5, 827-835 (2004)

slide8

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)

slide9

uORFS

1

2

3

4

GCN4

slide11

GCN4:

Non-starvation

Starvation

eif4e binding proteins 4e bp
eIF4E binding proteins: 4E-BP

Apoptosis

Insulin

AA (Leucine)

Cell Proliferation

slide15

IRE/IRP: steric hindrance

IRE-IRBP

Thomson et al. (1999) Intnl. J. Biochem & cell Biol. 31, pp 1139-1152.

sex lethal sxl
Sex-lethal: SXL

Ann-Bin Shyu. Nature Struct. & Molec. Biol. (2006) 13, 189-190.

viral ires
Viral IRES

X&Y=> IRES Trans-acting factors

Stoneley and Willis (2004) Oncogene 23, 3200-3207

slide18

IRES

Mechanisms of Internal Initiation

IRES

cap independent translation initiation
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
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
mRNA-rRNA base-pairing

Dresios et al. (2006) Nature Struct.& Mol. Bio. 13, 30-34.

summary
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)