RNA biology lecture 7

Question 1

Nuclear-cytoplasmic transport

Answer 1

• 5’ cap, 3’ polyA tail + PABP both protect + involved in export
• Next to have 3’ + 5’ UTR
• Export = interactions btw adaptors on RNA or sequence motifs on RNA cargo recognised by receptor molecule
• Nuclear pore complex forms basket structure in nuc, protruding filaments in cytoskeleton
• Porin proteins comprise nuclear pore, region that lack 2o form channel
• Pore allows small molecules to pass, carrier proteins needed for larger
• E needed to assemble diffusion competent complex

Question 2

Karyopherin family

Answer 2

• Traffic = dependent on these, act as exportins + importing
• E.g. cargo w/ export sequence recognised by exporting, assoc. w/ Ran-GTP, complex diffuses through pore → cyt
• In cyt, GAP binds Ran-GTP + hydrolyses GTP → disengages complex
• Ran-GEF imports Ran-GDP into nucleus + converted to Ran-GTP
• Ran-GTP used to release cargo imported to nucleus via importing

Question 3

Import/export of non-coding RNAs

Answer 3

• Exportins specific for ncRNA, also use karyopherin
• E.g. tRNA assoc. w/ exportin-t
• SnRNA exported by Phax/CRM1

Question 4

Export of mRNA/mRNPs

Answer 4

• mRNA exported from nuc→cytoplasm in Ran-GTP independent pathway
• Instead, use tap + p15 (TAP/Mex in yeast)
• Like Ran-GTP they associate w/ cargo
• Aly (part of EJC) = adaptor for export receptor TAP15
• TAP15 assoc w/ nuclear pore by interacting w/ component of nuclear pore complex
• SR/Aly-TAP15 translocate mRNA to nuclear pore

Question 5

Link between transcription, exosfome + mRNA transport

Answer 5

• Transcription apparatus has factors like SPT5/6 that deal w/ chromatin + exo factors involved in quality control
• In yeast, export complex is assoc w/ RNA pol II + may be deposited on mRNA co-transcriptionally
• Interaction btw TAP15 + Sac 3 = protein-protein interaction
• Gating effect by pulling out DNA of a particular gene toward nuclear pore
• E.g. SAGA recruited to promoter far from nuclear periphery

Question 6

RNA localisation

Answer 6

• Some RNAs localised to specific regions where needed
  E.g. = neurons (mRNA transported to axon into synapses, mRNA localis → polarisation)
  E.g. = migrating fibroblasts (localisation of B-actin mRNA to focal adhesion plaque, fibroblasts migrate along trajectory)
  E.g. epithelia (E-cadherin + b-actin mRNA localised)

Question 7

Transport of RNA

Answer 7

• Require specific 3’UTR sequences
• Proteins like ZBP-1 B-actin + MAP2 = adaptor that allow mRNP to assoc. w/ proteins for transport
• Other functions = prevent pre-mature assoc. of mRNA onto ribosome where mRNA shouldn’t be