The yeast nucleoporin Nup2p is associated primarily with the nuclear basket of
nuclear pore complexes and is required for efficient
importin-alpha:beta-mediated nuclear protein import as well as efficient nuclear
export of Kap60p/importin-alpha. Residues 1-51 of Nup2p bind tightly to Kap60p
and are required for Nup2p function in vivo. We have determined the 2.6 A
resolution crystal structure of a complex between this region of Nup2p and the
armadillo repeat domain of Kap60p. Nup2p binds along the inner concave groove of
Kap60p, but its interaction interface is different from that employed for
nuclear localization signal (NLS) recognition although there is some overlap
between them. Nup2p binds Kap60p more strongly than NLSs and accelerates release
of NLSs from Kap60p. Nup2p itself is released from Kap60p by Cse1p:RanGTP only
in the presence of the importin-beta binding (IBB) domain of Kap60p. These data
indicate that Nup2p increases the overall rate of nuclear trafficking by
coordinating nuclear import termination and importin recycling as a concerted
process.
