RANGTP-MEDIATED NUCLEAR EXPORT OF KARYOPHERIN-ALPHA INVOLVES ITS INTERACTION WITH THE NUCLEOPORIN NUP153

Using binding assays, we discovered an interaction between karyopherin alpha 2 and the nucleoporin Nup153 and mapped their interacting domai ns. We also isolated a 15-kDa tryptic fragment of karyopherin beta 1, termed beta 1, that contains a determinant for binding to the peptide repeat containing nucleoporin Nup98, In an in vitro assay in which ex port of endogenous nuclear karyopherin a from nuclei of digitonin-perm eabilized cells was quantitatively monitored by indirect immunofluores cence with anti-karyopherin alpha antibodies, we found that karyopheri n alpha export was stimulated by added GTPase Ran, required GTP hydrol ysis, and was inhibited by wheat germ agglutinin. RanGTP-mediated expo rt of karyopherin alpha was inhibited by peptides representing the int eracting domains of Nup153 and karyopherin alpha 2, indicating that th e binding reactions detected in vitro are physiologically relevant and verifying our mapping data. Moreover, beta 1, although it inhibited import, did not inhibit export of karyopherin alpha. Hence, karyopheri n alpha import into and export from nuclei are asymmetric processes.