FIG. 8.

Models for intranuclear translocation of SM. (A) Conventional model for CRM 1-mediated export of an NES-containing protein. CRM 1 is shown binding to soluble SM via its NES and transporting it to the NPC. CRM 1 docks at the NPC by binding to an FXFG nucleoporin-binding site (shown in gray). (B) Alternatively, CRM 1 binding detaches SM from its sites on the nuclear matrix or nuclear envelope (diagonal bars). Successive rounds of SM release and binding by CRM 1 constitute a possible mechanism of translocation along the nuclear matrix and through the NPC.