Nup2p is located on the nuclear side of the nuclear pore complex and coordinates Srp1p/importin-alpha export

Proteins bearing canonical nuclear localization sequences are imported into the nucleus by the importin/karyopherin-alpha/beta heterodimer, Recycling of the importin-alpha subunit to the cytoplasm requires the action of Gas, a member of the importin-beta superfamily. In the yeast Saccharomyces ceres ivisiae, the essential gene CSE1 encodes a Cas homologue that exports the y east importin-alpha protein Srp1p/Kap60p from the nucleus. In this report, we describe a role for the FXFG nucleoporin Nup2p, and possibly the related Nup1p, in the Cse1p-mediated nuclear export pathway. Yeast cells lacking N up2p or containing a particular temperature-sensitive mutation in NUP1 accu mulate Srp1p in the nucleus. Similarly, Cse1p is displaced from the nuclear rim to the nuclear interior in Delta nup2 cells. We do not observe any bio chemical interaction between Cse1p and Nup2p. Instead, we find that Nup2p b inds directly to Srp1p, We have localized Nup2p to the interior face of the nuclear pore complex, and have shown that its N terminus is sufficient for targeting Nup2p to the pore, as well as for binding to Srp1p, Taken togeth er, these data suggest that Nup2p is an important NPC docking site in the S rp1p export pathway.