Figure 1.

Nuclear import of cargo proteins implicates the recognition of a nuclear localization sequence (NLS) by importin receptors. In the nucleus, importins are dissociated from the cargo through the binding of Ran-GTP. Nuclear guanine-nucleotide exchange factors (GEFs) maintain elevated nuclear Ran-GTP concentration levels. On the other hand, translocation to the cytoplasm is facilitated by a nuclear export sequence (NES), recognized by exportin receptors such as CRM1 and further interacting with Ran-GTP. Upon translocation of the export complex to the cytoplasm, the cargo dissociates from the complex by means of GTPase-activating proteins (GAP)-mediated hydrolyzation of Ran-GTP to Ran-GDP.