RNA maturation transport & localization RNA export to the cytoplasm: model systems RNA degradation Links between RNA processing, transport, degradation.

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RNA maturation transport & localization RNA export to the cytoplasm: model systems RNA degradation Links between RNA processing, transport, degradation RNA localization in the cytoplasm RNA processing: brief overview

Evidence for checkpoints? mRNA transport All eukaryotic mRNAs are processed

Specific process for Pol II transcripts nuclear CBC binds to m 7 G-cap: role in splicing, transport, stability (exchanged in cytoplasm) Function in transport, stability, translation 1. Capping

CPSF: cleavage and polyadenylation specificity factor CStF: cleavage stimulatory factor CF: cleavage factor PAP: polyA polymerase PAB: polyA binding protein Function in transport, stability, translation 2. Polyadenylation

3. Splicing

Splicing is mediated by snRNPs

Compartments inside the nucleus 1. Nucleolus

2. Perichromatin granule clusters Carter et al., Science (1993) 259: 1330

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A. B. Casein mRNA prolactin ,000 mRNA/cell 300 mRNA/cell No change in transcription Examples of regulated mRNA turnover

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mRNA DECAY AAA m7Gppp poly A shorteningDeadenylase complex AAAAAAAAAAAAAAAA m7Gppp DecapitationDecapping enzyme (DCP1 complex) AAA 5’-3’ exonucleolytic cleavageXrn1 complex

Decay factors localize to cytoplasmic processing bodies (P bodies) Sheth et al. Science 2003

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RNA localization mRNA can be localized to subcellular compartments by actin or tubulin-dependent processes Examples: Xenopus: Vg1 mRNA (TGFb) 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

Examples of localized mRNAs in various systems

lamellipodia stainingperinuclear staining in myotubes 3’ UTR determins localization of many mRNAs

Bertrand et al., Mol Cell (98) 2: Ash1 mRNA specifically localizes to new daughter cells

Mechanism of Ash1 mRNA localization

SUMMARY I.mRNA decay - regulated and non-regulated turn-over but apparently coordinated - ordered pathways (e.g. deadenylation, decapping, exonucleolytic degradation) - cross-talk between translation and turnover - important regulation via non-coding RNAs - turnover occurs in specific cytoplasmic compartments - 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)