High levels of the GTPase Ran/TC4 relieve the requirement for nuclear protein transport factor 2.
The GTPase Ran/TC4 and the 14-kDa protein nuclear transport factor 2 ( NTF2) are two of the cytosolic factors that mediate nuclear protein import in vertebrates. Previous biochemical studies have shown that NTF2 binds directly to the GDP- bound form of Ran/TC4 and to proteins of the nuclear pore complex that contain phenylalanine-glycine repeats. In the present study we have used molecular genetic approaches to study the Saccharomyces cerevisiae homologue of NTF2. The scNTF2 gene encodes a protein that is 44% identical to the human protein. We found that deletion of the scNTF2 gene is lethal and that repression of NTF2p expression by a regulatable promoter results in gross structural distortions of the nuclear envelope. In a screen for high copy number suppressors of a scNTF2 deletion, the only gene we isolated other than scNTF2 itself was GSP1, the S. cerevisiae homologue of Ran/TC4. Furthermore, we found that high levels of Ran/TC4 can relieve the requirement for NTF2 in a mammalian-permeabilized cell assay for nuclear protein import. These data suggest that certain of the nuclear protein import functions of NTF2 and Ran/TC4 are closely linked and that NTF2 may serve to modulate a transport step involving Ran/TC4.[1]References
- High levels of the GTPase Ran/TC4 relieve the requirement for nuclear protein transport factor 2. Paschal, B.M., Fritze, C., Guan, T., Gerace, L. J. Biol. Chem. (1997) [Pubmed]
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