NUCLEOCYTOPLASMIC TRANSPORT

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This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Nucleocytoplasmic transport of proteins and nucleic acids is crucial for normal cell functioning. It occurs by way of nuclear pore complexes and is controlled by a small GTPase, Ran. Two recently proposed models (Smith et al., Science (2002), Gorlich et al., EMBO J (2002)) predict very different sensitivity of the Ran nucleocytoplasmic transport to the activity of the Ran guanine exchange factor, RCC1, an enzyme converting Ran to the GTP-bound form in the nucleus. A comparative analysis of the models shows that they are structurally similar but assume somewhat different enzyme activities and, particularly, 20-fold different pore permeability for the Ran entry into the nucleus. Fluorescence correlation spectroscopy (FCS) in live cells is being used to directly measure reaction rates and mobile fractions of components in this pathway to assess which of these models best fit the experimental situation.