Nucleo-Cytoplasmic Exchange

ID #1213

Just curious about the shuttle proteins (importin and exportin). Since they can get in and out of the nucleus, that means they must have their own NLS and NES, right? Because Exportin seems to get into the nucleus all by itself, thus there must be some reason how it manages to do that. I'm just trying to see whether the "signal rule" applies for all proteins; even the ones that carry other proteins.

Great question! You're absolutely right that an exportin that finds itself out in the cytoplasm is going to need to get back into the nucleus. And you're also right that proteins don't get across the nuclear pore unless they display an appropriate signal. So... it seems logical that importins need an NES and exportins need an NLS to get "back." But in reality, the signals that these carriers present aren't standard NLS or NES's. They've actually got their own unique signals that allow them to be moved back and forth, so you don't need an importin to accompany an exportin back into the nucleus!

This was a very good connection that you made; it just happens to be a little different than one might guess.

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