| Description |
Communication between the nucleus and the cytoplasm is dependent upon transport across the double membrane of the nuclear envelope. All traffic between the nucleus and cytoplasm occurs at large proteinacious structures embedded within the nuclear envelope called nuclear pore complexes (NPCs). Trafficking of a wide array of cargo necessitates that individual pore proteins coordinately function with localization signals, receptors, and accessory factors to mediate propel-transport events. Although much is known about the soluble machinery that is required for nucleocytoplasmic transport, little is known about how individual nucleoporins contribute to this process. One nucleoporin, Nup153, is a central regulator of transport. Overexpression of a C-terminal fragment of Nup153 in cultured cells causes the accumulation of poly(A)+ RNA in the nucleus, suggesting a role for Nup153 in mRNA export. Moreover, specific perturbation of Nup153 in vivo results in the prevention of several classes of RNA, including mRNA, from being exported. The goal of this dissertation is to define how the property of RNA association contributes to the function of this pore protein. I have examined the interaction of Nup153 with RNA and identified a novel RNA binding domain within this pore protein that is sufficient to mediate this property. My studies indicate an important functional attribute of RNA association, as this domain is functionally conserved through evolution. I have also assisted in further characterizing Nup153's RNA binding properties and we have found that Nup153 shows a preference for single-stranded RNAs that lack structure. Unstructured stretches of single-stranded RNA are defined to be mRNA identity elements and raise the possibility that the RNA binding domain of Nup153 acts as an interface with mRNA. To better define the RNA determinants that mediate Nup153 recognition, we have established minimal length and base composition requirements. Our findings show for the first time that binding of RNA substrates by a nucleoporin can be correlated with nuclear export. In addition, I contributed to a project focused on Nup153 nuclear mobility and we found that dynamics of this pore protein in the nucleus is dependent upon on-going transcription, supporting a connection between Nup153 function and mRNA production. |
