The nuclear pore complex (NPC) is a huge structure (approximately 120 MDa in metazoans) that spans the nuclear envelope, bridging the nucleus to the cytoplasm. A diverse array of cargo is trafficked through the pore, each cargo type upholding specific requirements for transport. Although all nucleocytoplasmic trafficking is known to converge at the NPC, specific routes and mechanisms of passage through the pore are not well understood. The broad, long-tern objective of this research is to contribute to an understanding of the mechanistic role of nuclear pore proteins in the transport of cargo through the NPC. The pore protein Nup 153 has been shown to have a central role in the export of several types of RNA in vivo, as well as maintain stable association with RNA in vitro. The aims of this thesis will, therefore, address the following: (1) The domain within Nup 153 that confers RNA association will be identified and characterized using an in vitro binding assay. (2) In vitro binding assays and protein interaction screens will be used to establish the. physiological targets of Nup153. (3) Finally, the role of association between RNA and Nup153 will be studied in vivo using Xenopus oocyte microinjection. Such experiments will lead to an understanding of Nup153's functional role in RNA export. Nucleocytoplasmic transport processes, such as RNA export, are often deregulated in virally-infected cells. Understanding how nuclear pore proteins such as Nup153 function will be important not only in understanding how the mechanics of transport contribute to normal cell function, but also in understanding how to prevent viruses from circumventing these normal control mechanisms.