Nuclear transporters importins

Bischoff, F.R. and Gorlich, D. (1997) RanBPl is crucial for the release of RanGTP from importin -related nuclear transport factors. FEBS Lett., 419, 249-254. 

Fig. 10.7 Nuclear transport proceeds through core complexes and is mediated by transport receptors of the Importin p-family. These receptors interact with the nuclear core complexes and shuttle between the nucleus and the cytoplasm. (Reproduced with permission of Elizabeth Pennisi and Science from the model in ref. 63.)...

Using this assay system, four required proteins were purified Ran, nuclear transport factor 2 (NTF2), im-portln a, and Importln p. Ran is a monomeric G protein that exists in two conformations, one when complexed with GTP and an alternative one when the GTP is hydrolyzed to GDP (see Figure 3-29). The two importins... 

Importins are transport proteins at the nuclear pore complex, needed for the selective import of proteins into the nucleus. They recognize nuclear localization signal sequences of cargo proteins. 

Sequence of amino acids that determine the transport of proteins into the nucleus. Although there is no clear consensus, nuclear localization signals tend to be rich in positively charged residues, which allow interaction with proteins from the nuclear import machinery (i.e., importins). 

The nuclear envelope is perforated with huge macromolecular assemblies of 30 different proteins that form nuclear pore complexes with a central channel of 25-30 nm in diameter. This channel allows proteins smaller than 30 kDa to passively traverse the outer and inner nuclear membranes. Larger proteins are actively transported across the nuclear envelope and contain nuclear localization signal (NLS) sequence motifs. These signals consist of one or two clusters of four or five basic residues localized usually within the polypeptide chain. The import of proteins with NLS through the channel is facilitated by the carrier heterodimer of importin-a ( > (Gorlich and Kutay 1999 Pemberton and Paschal... 

There are some transport pathways for mRNA export which do not require an importin/3 family member. Mex67/TAP is a factor with a direct role in mRNA export (Strasser and Hurt, 2000 Stutz et al., 2000 Nakielny and Dreyfuss, 1999). Mex67/TAP binds RNA and Nups and has the ability to undergo nucleocytoplasmic shuttling. Another factor might be involved (Hodge et al., 1999). How the actions of these factors are coordinated to mediate mRNA export is presently unknown. Once recognized by the export machinery, RNAs must transverse the nuclear pore. 

Immunostimulation, 469 Importin-mediated nuclear import, 231 Inducible gene expression, 15 Integrin targeting, 349 Intramuscular gene delivery, 285 Ischemic heart disease (IHD), 500 Intravascular delivery, 489 Interstitial transport, 434 Intratumoral infusion, 436 Intion, 2... 

Importins Transport Proteins Containing Nuclear-Localization Signals into the Nucleus... 

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