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- Critical Read/of Outstanding Interest (oo)
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- (o)(Ref 3, LeHir, et al) A good overview on how introns may influence gene expression, and why the EJC (Exon Junction Complex) is such an important player in the "mRNA to translation steps" in the control of gene expression.
- (o)(Ref4, Tange, et al)) Great Review on EJC, and a relatively quick read (five to ten minutes).
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- of the Breast Cancer Protein MLN51 with the Exon Junction Complex via Its Speckle Localizer and RNA Binding Module []
Unresolved Questions for Followup
(Homework) Discussion Topics /Questions
Paper for additional Discussion (2 figures presented in EJC presentation on Thurs. 31 May 2007):
- Noble CG, Song H (2007) MLN51 Stimulates the RNA-Helicase Activity of eIF4AIII. PLoS ONE 2(3): e303. doi:10.1371/journal.pone.0000303[]
- Can post a comment on PLos (Public Library of Science) for everyone in the world to discuss the positive aspects, as well as limitations of this paper.
- Assuming that Y14 and Magoh inhibit ATP hydrolysis and in the ATP bound form eIF4AIII binds the mRNA tightly, why might such a fragile system be favorable?
Perhaps the inhibition of ATP hydrolysis by Magoh and Y14 lends the complex to be primed to uncouple from the mRNA in the pioneering translation round.
- If MLN51 (Btz) stimulates ATP hydrolysis, and Y14/Magoh inhibits would you expect an ordered binding of these subunits to eIF4AIII?
This is pure speculation but since there are competing forces (activators and inhibitors )perhaps there is some interplay and one might go so far to say that there MAY even an sequential binding.
- Why didn't the authors further verify their "large conformational change" with an additional in vitro experiment (rhetorical)?
Q1. The authors down play the observation that the RNA is in a bent conformation. Why might this actually be important?
A1. The bent conformation observed for the bound polyU RNA may help explain why the EJC complex binds specifically at exon junctions. The spliceosome bends RNA through out the splicing cycle. The EJC complex may therefore bind at particular bends imposed by the spliceosome - this would lower the entropic cost of binding for the EJC complex.
Q2. Suggest some possible experiments to test the observed protein-protein interaction network and it's effect on assembly on RNA?
A2. As for all x-ray crystal structures, the crystallographers or collaborators should make an attempt to support their structure using experiments in solution. This is particularly important when characterizing protein-protein interactions, where point mutations should be made at sites thought to be important from the crystal structure and tested in a solution based assay. This helps to rule out crystal packing artifacts, a somewhat common artifact of shoving proteins together to form a crystal lattice. The authors unfortunately did not do this for the EJC crystal structure. GST pull down assay and native PAGE using radiolabeled RNA could be used to test important contacts, and investigate potential cooperativity between protomers in the EJC complex as it forms on RNA.
Faculty Questions and Comments