![]() ![]() Nuclear pores allow the rapid movement of macromolecules in both directions. Similar types of transport receptors, operating in the reverse direction, export mRNAs from the nucleus. These prospective nuclear proteins are escorted into the nucleus by nuclear import receptors, which then return to the cytosol for reuse. It is required for the first stage of sperm chromatin decondensation. Newly made proteins that are destined for the nucleus must also be imported from the cytosol. Nucleoplasmin has at least one other role in modulating chromatin structure in Xenopus eggs. RNA molecules, which are synthesized in the nucleus, and ribosomal subunits, which are assembled there, must be exported to the cytosol. Selected larger molecules and macromolecular complexes also need to pass through nuclear pores. Many of the proteins that line the nuclear pore contain extensive, unstructured regions that form a soft, tangled meshwork this meshwork fills the center of the channel, preventing the passage of large molecules but allowing small, water-soluble molecules to pass freely and nonselectively between the nucleus and the cytosol. A nuclear pore is a large, elaborate structure composed of a complex of about 30 different proteins, each present in multiple copies. The qualitative vector analysis of Imp -NplNLS NM8/PC2 indicated a combination of two motions, characterized by a lateral bending tendency (based on a 90° X-axis rotation of Imp in relation to the bending orientation in NM7/PC1) in ARMs 16, mixed with a twist in ARMs 710 ( Fig 3, S12 Fig and S2 Movie ). Proteins with a nuclear localization signal enter at the same time that proteins with a nuclear export signal exit. Nuclear import receptors are exported to the cytosol. Nuclear import receptors enter from the cytosol. mRNA molecules are exported to the cytosol. ![]()
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