Question

Topic: Nuclear Transport

NES ОО 5 (a)

1) What protein will be the “prey”? That is, if the NES in your newly-discovered protein functions in the typical nuclear export pathway shown in the schematic, what protein will bind to the NES to mediate its export from the nucleus?

2) What protein (shown in the schematic) will dissociate the protein-NES complexassuming typical exportin mediated export?

3) Fill out the schematic of the Coomassie-stained SDS-PAGE gel to illustrate the expected results if you used the tag-fragment fusion proteins listed; assume the NES in your newly-discovered protein functions in the typical NES-mediated nuclear export pathway?

Answer 1

Nucleus in a eukaryotic cell is a double membrane bound organelle, which holds the DNA. Nuclear pore complexes present in the nuclear membrane mediate the exchange of material between the cytosol and the nucleus.

Protein destined for the nucleus are synthesized completly on the ribosomes present in the cytosol. They bear a Nuclear localization signal which mediates its translocation to the nucleus.

The nuclear protein import and export is mediated by importins and exportins.

These proteins bind to the nuclear import signal (NIS) and the nuclear export signals (NES) respectively.

An exportin recognizes and binds to NES present on the cargo protein. Ran/ GTP binds to this complex and strengthens the stability of the complex. This complex is now transported to the nuclear pores and exported out. In the cytoplasm GTP is hydrolyzed by Ran GAP (GTPase activating protein) and this causes Ran/ GDP to leave. This causes dissociation of the exportin and cargo protein complex.

Answer. Exportin binds to the NES of the newly discovered protein.