Importin beta validates human importin beta as a cell cycle negative regulator-4

In beta with 94% identities (828/876, black boxes) and 97% positives (857/876 gray and black boxes). The amino acid composition, along with the length of the protein, is well conserved between and human importin beta. Three of the conservative amino acid differences between the and human importin beta sequence are at residues involved in FG-domain binding (F217Y [82–84], I265V [], and L505V []).<p><b>Copyright information:</b></p><p>Taken from "importin beta validates human importin beta as a cell cycle negative regulator"</p><p>http://www.biomedcentral.com/1471-2121/9/14</p><p>BMC Cell Biology 2008;9():14-14.</p><p>Published online 22 Mar 2008</p><p>PMCID:PMC2324082.</p><p></p

Importin beta validates human importin beta as a cell cycle negative regulator-3

D importin beta were not able to assemble nuclear pores (+Tag-X-β). When RanQ69L-GTP was added along with His-tagged importin beta, the block to pore assembly could not be reversed (+Tag-X-β +Ran). Where indicated, importin beta was added at 10 μM and RanQ69L-GTP at 50 μM. The bar represents 10 microns. Pore-free BAPTA nuclear intermediates rescued in the presence of cytosol and untagged human or importin beta were not able to assemble nuclear pores (+X-β or +h-β). The inhibitory concentration of 10 μM used here was determined to be the approximate minimum concentration for pore assembly inhibition in a separate experiment (data not shown). When RanQ69L-GTP was added along with untagged human importin beta, the block to pore assembly was partially reversed (+h-β +Ran). The importin beta block was fully reversed (+X-β +Ran). To better visualize the FG-nucleoporin stain, a section of the images (white dashed box) was enlarged by 3X (right most panel). Where indicated, importin beta was added at 10 μM and RanQ69L-GTP at 50 μM. The bar represents 10 microns.<p><b>Copyright information:</b></p><p>Taken from "importin beta validates human importin beta as a cell cycle negative regulator"</p><p>http://www.biomedcentral.com/1471-2121/9/14</p><p>BMC Cell Biology 2008;9():14-14.</p><p>Published online 22 Mar 2008</p><p>PMCID:PMC2324082.</p><p></p

Transportin Regulates Major Mitotic Assembly Events: From Spindle to Nuclear Pore Assembly

Mitosis in higher eukaryotes is marked by the sequential assembly of two massive structures: the mitotic spindle and the nucleus. Nuclear assembly itself requires the precise formation of both nuclear membranes and nuclear pore complexes. Previously, importin alpha/beta and RanGTP were shown to act as dueling regulators to ensure that these assembly processes occur only in the vicinity of the mitotic chromosomes. We now find that the distantly related karyopherin, transportin, negatively regulates nuclear envelope fusion and nuclear pore assembly in Xenopus egg extracts. We show that transportin—and importin beta—initiate their regulation as early as the first known step of nuclear pore assembly: recruitment of the critical pore-targeting nucleoporin ELYS/MEL-28 to chromatin. Indeed, each karyopherin can interact directly with ELYS. We further define the nucleoporin subunit targets for transportin and importin beta and find them to be largely the same: ELYS, the Nup107/160 complex, Nup53, and the FG nucleoporins. Equally importantly, we find that transportin negatively regulates mitotic spindle assembly. These negative regulatory events are counteracted by RanGTP. We conclude that the interplay of the two negative regulators, transportin and importin beta, along with the positive regulator RanGTP, allows precise choreography of multiple cell cycle assembly events