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Unformatted text preview: GTPase in the cytosol and in the nucleus? (2 point) (Mostly) GTP ­bound in both compartments. Explain in mechanistic terms what happens to protein nuclear IMPORT in cells that have RanGAP inactivated. (4 points) Since Ran is GTP ­bound even in the cytosol, importin will NOT bind import cargo in the cytosol. This is because Ran ­GTP competes with import cargo for binding to importin (with Ran ­GTP winning). Without binding importin, import cargo will not be imported into the nucleus (i.e., no nuclear import). Explain in mechanistic terms what happens to protein nuclear EXPORT in cells that have RanGAP inactivated. (4 points) Since Ran is still GTP ­bound in the nucleus, exportin can still simultaneously bind to export cargo and Ran ­GTP. When this complex reaches the cytosolic side of the nuclear pore, there is no active RanGAP to cause Ran to hydrolyze its GTP. As a result, the export cargo does not dissociate from exportin in the cytosol. Hence, nuclear export becomes defective. (In p...
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