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Nucleocytoplasmic transport and transport in confined media

The extensive and multifaceted traffic between nucleus and cytoplasm is handled by a single type of macromolecular assembly, the nuclear pore complex (NPC). While some molecules, such as ions and metabolites, need to constantly transport between nucleus and cytoplasm, the traffic of others, namely of proteins and RNAs, must be tightly controlled as their unscheduled nuclear entry or exit could be highly detrimental. Thus, each NPC must be continuously conductive to certain molecules and at the same time impermeable to others. This is true for traffic taking place from nucleus to cytoplasm and from cytoplasm to nucleus. Given that some of the cargoes that cross the NPC can be quite large, e.g., certain mRNPs or ribosomal subunits, achieving the task of being open and closed simultaneously, and for cargo from opposite directions, requires some engineering ingenuity. We are interested in the way the NPCs discriminate between ‘permissive’ (i.e. nuclear transport receptors) and ‘barred’ macromolecular cargoes, in the way it coordinates traffic occurring in two directions, and in the way it coordinates traffic of small and large molecules. More broadly, we are interested in the dynamics of transport processes occurring in confined media. To tackle these issues we make use of bulk and single-molecule fluorescent microscopy techniques as well as non-equilibrium statistical mechanics simulations. In a more application-oriented direction, we are developing methods to efficiently and specifically target therapeutic DNA molecules, delivered by synthetic carriers, to the cell nucleus. We use a piggyback approach in which we modify the DNA sequence by binding sites for transcription factors that naturally carry nuclear localization signals which are recognized by nuclear import receptors. Focusing on transcription factors which aberrantly shuttle to the nucleus in certain cancerous cells, we hope to achieve therapeutic specificity that can be subsequently utilized for suicide gene therapy.

AFM images of NPCs scanned along their cytoplasmic (A-C) and the nuclear (D-F) sides.
Receptor(NTR)-mediated protein nuclear import and export
totally assymetric exclusion principle model for coordination of bi-directional traffic through the NPC
increasing cargo surface hydrophobicity is sufficient to compromise NPC permeability barrier
pDNA modified by NFκB binding sites for piggy-back nuclear import
nuclear entry of κB-modified pDNA

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Last updated November 2013