rna localization
DESCRIPTION
RNA localization. mRNA can be localized to subcellular compartments by actin or tubulin -dependent processes. Examples :. Xenopus : Vg1 mRNA (TGF b ) to vegetal pole. Drosophila : nanos, oskar mRNA (posterior) and bicoid (anterior). (requires mRNA binding protein staufen). - PowerPoint PPT PresentationTRANSCRIPT
RNA localizationmRNA can be localized to subcellular compartmentsby actin or tubulin-dependent processesExamples:
Xenopus: Vg1 mRNA (TGF) to vegetal pole
Drosophila: nanos, oskar mRNA (posterior) and bicoid (anterior)
(requires mRNA binding protein staufen)
(requires staufen and miranda)
prospero (into ganglion of mother cells; neuroblast TF)
Yeast: Ash1 mRNA to daughter cell
SUMMARY 2
I. mRNA decay- regulated and non-regulated turn-over- ordered pathway (deadenylation, decapping, exonucleolytic degradation)- NMD: recognition of premature stop codons
II. Cytoplasmic mRNA localization- ZIP code in 3’ UTR- both actin and tubulin-mediated - yeast mating type switch as a model: Ash1 mRNA localization (via 3’ UTR, She2/3, Myo4 and actin cables)
N
N
N
O
N
NH2
H
N
N
N
N H
O
O
HN Ala 151
HN Ala 151
O
O
C Asp 125
Val 124
Lys 123
Asn 122
NH3+
O
H2N
C Asn 125
Val 124
Lys 123
Asn 122
NH3+
Ran WTRan WT
Ran D125NRan D125N
GTPGTP
XTPXTP
In vitro reconstitution of ER translocation:
- Sec61 complex: conserved translocation channel Sec61 subunits () Sec62/63 TRAM (translocating chain-assoc. membrane protein)
- phospholipids (proteoliposomes) and luminal chaperones (BIP)
- SRP/SRP receptor only required for co-translational translocation not for post-translational translocation (e.g pre-pro-alpha factor).
- energetics of translocation: protein conducting channel (cotranslational) molecular ratcheting (posttranslational)
ER function
- Proper folding of proteins (chaperones, lectins, petidyl-prolyl-isomerases)- Formation of disulfide bonds (PDI) GSH prevents oxidation in cytosol GS-SG + NADPH + H+ <=> 2 GSH + NADP+
- Proteolytic cleavages- Addition & processing of carbohydrates- Assembly into multimeric proteins
- Ca2+ storage- Lipid synthesis- Detoxification (liver!)
Summary
ER translocation: SRP-dependent and -independent pathways; translocation occurs through Sec61 complex; topogenic sequences determine overall orientation.
ER function
Compartmental identity: maturation versus fixed compartments
Identification of components: combination of genetics, biochemistry...
Vesicular coats: COPI ~ retrograde: Golgi->ER COPII ~anterograde: ER->Golgi CCV post-Golgi, various adaptors