BIO206 Lecture 20/22.pdf

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1 Dec 2013
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- signal sequence is required for transport into the nucleus. The sequence is generally 1-2
positively charged areas (lysine or arginine) - REFER TO TABLE IN YOUR TEXT
- initial interaction with the pores requires aid of NUCLEAR IMPORT RECEPTORS - these
bind and then interact with the fibrils, directing the protein into the pore
- the pore opens just enough to allow the complex of protein and NIR to enter, and then
closes. GTP hydrolysis is required for this change but the exact mechanism is still unknown.
NLS - Localization is in the body of the protein
-
- the NIR dissociates in the nucleus and is transported back out of a nuclear pore to the
cytoplasm (recycled)
Signal Sequences
Lecture 20/ 22
November-13-13
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- this diagram is in your textbook and you can see the schematic shows the various steps
- protein binds, the complex is transported through, then they separate and the NUCLEAR
IMPORT RECEPTOR is recycled back out to the cytosol to collect another protein.
Note that in the nuclear to cytosol direction you don’t seem to need a NIR equivalent.
- FULLY FOLDED proteins and ASSEMBLED ribosomal subunits are tranported - in order
for proteins to enter the other organelles they must be UNFOLDED - as we will see next.
Releasing of the protein is a catalyzed reaction
It has higher affinity for the binding site than the transport protein
-
RAN - a member of GTP binding protein
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It has higher affinity for the binding site than the transport protein
-
Another protein hydrolyzes, the hydrolysis results in the release of RAN protein
RAN participates in export of protein to cytoplasm
The whole protein with nuclear export signal has a higher affinity for the export process
RAN GTP is moving unidirectional (this is a problem)
Essential Cell Biology (ECB3) Alberts et al.
Chapter 15: pages 505 - 509
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Document Summary

Signal sequence is required for transport into the nucleus. The sequence is generally 1-2 positively charged areas (lysine or arginine) - refer to table in your text. Initial interaction with the pores requires aid of nuclear import receptors - these bind and then interact with the fibrils, directing the protein into the pore. The pore opens just enough to allow the complex of protein and nir to enter, and then closes. Gtp hydrolysis is required for this change but the exact mechanism is still unknown. The nir dissociates in the nucleus and is transported back out of a nuclear pore to the cytoplasm (recycled) Nls - localization is in the body of the protein. This diagram is in your textbook and you can see the schematic shows the various steps. Protein binds, the complex is transported through, then they separate and the nuclear. Import receptor is recycled back out to the cytosol to collect another protein.

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