Figure 4.

CRM1 promotes the export of snurportin 1 from the nucleus. Nuclear import of 1.6 μM fluorescein-labeled snurportin 1 and 1.6 μM Texas red–labeled importin α was allowed for 10 min in the presence of importin β (0.7 μM) and nucleoplasmin (1.4 μM) as described in Materials and Methods. After 10 min, one aliquot of the sample was fixed. The remaining sample was split in three. Either 3 μM CRM1, 3 μM CAS, or buffer was added and the incubation was continued for another 10 min before fixation. Nuclei were spun onto coverslips and fluorescent proteins were detected by confocal microscopy (63× oil objective). Note that addition of CRM1 specifically leads to a depletion of the intranuclear snurportin 1 and the appearance of an NPC staining, but had no effect on importin α distribution. In contrast, CAS promoted export of importin α, but not of snurportin.