Communication between the nucleus and cytoplasm is mediated by large proteinaceous structures embedded in the nuclear envelope, the nuclear pore complexes (NPCs). The most outstanding issue in the nuclear transport field involves delineating how a transporting complex moves through the aqueous channel of the NPC. The long range goal of this project is to understand the role of the NPC in nuclear transport at the molecular level.
The aims i n this proposal are specifically directed at dissecting the network of structural network of structural interactions that mediate two aspects of nuclear export: the recycling of beta import factors and poly(A)+ RNA export. A critical point in these nuclear export pathways is to analyze the mechanism for the export of beta transport factors in the yeast Saccharomyces cerevisiae. Studies will be conducted to analyze the structural determinants in the GLFG region of the nucleoporin Nup116p that are required for interaction with the beta Kap95p, and new strategies will be employed to reveal other essential steps in the export mechanisms. In the second and third aims, we will analyze the mechanism of action of two potential RNA export mediators: Gle1p and Gle2p. These proteins are both prime candidates for bridging interactions between the RNA-protein transport substrate and the NPC. To investigate how Gle2p mediates the assembly of RNA export machinery, we will define the structural basis of the Gle2p-Nup116p interaction, and biochemically identify other Gle2p- binding partners. To explore the role of Gle1p in the export of poly(A)+ RNA, we will expand our research program with the combined study of both yeast Gle1p and a recently identified human Gle1p. We will test whether the nuclear export sequences in yeast and human Gle1p are utilized for nucleocytoplasmic shuttling, and map the Gle1p structural determinants that are responsible for NPC interaction and nuclear export dynamics. By identifying factors that interact specifically with yeast and/or human GLE1P, we predict that both conserved and distinct aspects of the export machinery across species will be revealed. The experimental methods in all the aims are designed to benefit from the strength of combining molecular genetic, biochemical, and cell biological approaches. Together these studies are expected to elucidate the sequence of events required for the nuclear exit of a beta transport factor and a RNA-protein complex through the NPC. This analysis is the next step necessary for providing key insights into the general mechanism for movement through the NPC portal.
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