Fig. 4. SRP19 is imported into the nucleus by importin 8 and transportin. Recombinant human rpL23a or human SRP19 were purified, labeled with fluorophores and used as substrates (2 µM final concentration) for import into the nuclei of permeabilized HeLa cells. Import receptors were also used at 2 µM, except importin 
(imp) and importin 8 (imp 8), which were both at 4 µM. Reactions were stopped by fixation after 10 minutes for SRP19 and 25 minutes for rpL23a and analyzed by confocal microscopy. As previously reported, rpL23a could be imported by any of four transport receptors: importin ß (impß; C), transportin (trn; D), importin 5 (imp5; E), and importin 7 (imp7; F) (Jäkel and Görlich, 1998). SRP19 import was most efficient with importin 8 (imp8; G); however, transportin also mediated nuclear import of SRP19 (D). All images were collected and analyzed as described in Fig. 1. Bar, 10 µm.
