Transport Of Macromolecules

Nuclear transport is an energy-dependent process mediated through saturable receptors. Export and Import receptors are by to recognize and bind to nuclear localization signals or nuclear export signals respectively in the transported molecules. Receptor-substrate communication can be direct or mediated through a further adapter protein. Transport receptors dock their cargoes to the nuclear pore complexes that are also known as NPC and facilitate their translocation via the NPC. After delivering their cargoes, the receptors are recycled to initiate further rounds of transport. Since a transport event for a cargo molecule is unidirectional the transport receptors engage in asymmetric cycles of translocation across the NPC.

The GTPase Ran behaves as a molecular trigger for receptor-cargo directionality and interaction to the transport process. Presently, the combined use of variant in vitro and in vivo approaches has led to the characterization of novel export and import signals and to the recognization of the first nuclear import and export receptors. The Passive transport of macromolecules in growing nerve procedures was analyzed quantitatively through measuring the rate of diffusion of fluorescently labeled molecules injected into the soma of cultured Xenopus neurons. We found in which the diffusion of globular proteins in the neurite's cytoplasm was about five times slower than which in aqueous solution and a rate considerably higher than those inferred from past studies on cultured non-neuronal cells.