SILAC-Tp (12 importins) - Extensive cargo identification reveals distinct biological roles of the 12 importin pathways

Importin-beta family proteins are nucleocytoplasmic transport receptors (NTRs), and they transport most nuclear proteins as their cargoes into and out of the nuclei. Human cells have 20 species of importin-beta family NTRs, of which 10 (importin-beta, transportin-1, -2, -SR, importin-4, -5, -7, -8, -9, and -11) are nuclear import receptors and 2 (importin-13, and exportin-4) are bi-directional receptors. Here, we identified the import cargo proteins of these 12 NTRs by a method called SILAC-Tp, which employs stable isotope labeling with amino acids in cell culture (SILAC), an in vitro reconstituted transport system, and LC-MS/MS.