The nucleoporin Nup153 plays a critical role in multiple types of nuclear export

The fundamental process of nucleocytoplasmic transport takes place through the nuclear pore. Peripheral pore structures are presumably poised to inter act with transport receptors and their cargo as these receptor complexes fi rst encounter the pore. One such peripheral structure likely to play an imp ortant role in nuclear export is the basket structure located on the nuclea r side of the pore. At present, Nup153 is the only nucleoporin known to loc alize to the surface of this basket, suggesting that Nup153 is potentially one of the first pore components an RNA or protein encounters during export . In this study, anti-Nup153 antibodies were used to probe the role of Nup1 53 in nuclear export in Xenopus oocytes. We found that Nup153 antibodies bl ock three major classes of RNA export, that of snRNA, mRNA, and 5S rRNA. Nu p153 antibodies also block the NES protein export pathway, specifically the export of the HIV Rev protein, as well as Rev-dependent RNA export. Not al l export was blocked; Nup153 antibodies did not impede the export of tRNA o r the recycling of importin beta to the cytoplasm. The specific antibodies used here also did not affect nuclear import, whether mediated by importin alpha/beta or by transportin. Overall, the results indicate that Nup153 is crucial to multiple classes of RNA and protein export, being involved at a vital juncture point in their export pathways. This juncture point appears to be one that is bypassed by tRNA during its export. We asked whether a ph ysical interaction between RNA and Nup153 could be observed, using homoribo polymers as sequence-independent probes for interaction. Nup153, unlike fou r other nucleoporins including Nup98, associated strongly with poly(G) and significantly with poly(U). Thus, Nup153 is unique among the nucleoporins t ested in its ability to interact with RNA and must do so either directly or indirectly through an adaptor protein. These results suggest a unique mech anistic role for Nup153 in the export of multiple cargos.