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Anatomy & Cell Biology
ANAT 262
John Presley

- direction of RNA transport all have trafficking aided by transporters - mRNA will not be exported if it is not spliced (also needs 5’ cap and 3’ poly A tail but those are less important) - transcript in nucleus contains introns which have nuclear retention signal so un- til splice they will not be shuttled to the cytoplasm - no TAP involved with viral mRNA - virus has an RRE which REV binds to (REV contains a nuclear export signal) so if Crm1 binds to REV we have nuclear export - REV protein binds to RRE which has hydrophobic export signal which is recog- nized by Crm1 - drug LMB interferes with Crm1 functioning and causes disappearance of virus but cells die as it is not specific and prevents export of other important molecules - creating mutant REV with non-working NES would prevent export - looking for drug to prevent REV binding to RRE - DDX19 is the human version of Dbp5p which needs to be on RNA for Tap to export it - viruses use DDX3 to get mRNA out via crm1 - drugs that target DDX3 could stop this process, but DDX3 is used in other pro- cesses as well RNA helices give energy for RNA export - protein trafficking uses Ran, mRNA export uses RNA helices Mutation of a single RNA exporter (GLE1) causes malformation of a fetus mouth and limbs to attach in the wrong places Post-translation import of proteins into different organelles requires chaperones in the cytoplasm and organelle - to get into the perioxisomal or mitochondrial matrix you need signals, energy, and cel- lular import apparatus (machinery to mediate trafficking) Peroxisome: single membrane surrounds the peroxisomal matrix - plays a role in many detoxification reactions (the enzyme catalase oxidizes different compounds and removes H2O2 which is made during non-metabolic processes) - B-oxidation of long chain fatty acids (degrades them) - Involved in synthesis of plasmalogens (lipids that make myelin) - closely associated with the ER Peroxisomes could be generated by: - budding from the ER - fission: imports more proteins into already made perioxisomes and then splits into two - no transcription/translation occurs in peroxisomes - uses ATP for energy - yarrowia yeasts generate peroxisomes when given lipids - 90% have SKL sequence at C terminus (this can stay or be cleaved) - 10% have PTS-2 at N terminus (this must be cleaved) 1) fold protein in the cytoplasm 2) protein associates with receptor (PEX5 for PTS1 or PEX7 for PTS2) 3) move onto docking site (this is energy independent and must occur at 4 degrees cel- sius) 4) move inside matrix (this needs energy = ATP) 5) dissociate complex and bring receptor back out - pore consists of several PEX proteins which bind to PEX5 or PEX7 - docking site recognizes the receptors - PEX5 and cargo go into the matrix (receptor is shuttled back out) - the docking site transiently opens after the cargo and carrier bind which creates a pore
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