Abstract
The objective of this investigation was to determine whether there is mediated transport of endogenous proteins across the nuclear envelope. For this purpose, we studied the nuclear uptake of a 148,000-dalton Rana oocyte polypeptide (RN1) and compared its actual uptake rate with the rate that would be expected if RN1 crossed the envelope by simple diffusion through the nuclear pores. Nuclear uptake was studied in two ways: first, oocytes were incubated in L-[3H]leucine for 1 h and, at various intervals after labeling, the amount of 3H-RN1 present in the nucleoplasm was determined. Second, L-[3H]leucine-labeled nuclear extracts, containing RN1, were microinjected into the cytoplasm of nonlabeled cells, and the proportion of 3H-RN1 that subsequently entered the nucleus was measured. It was found that RN1 can readily penetrate the nuclear envelope; for example, after 6 h, approximately 36% of the newly synthesized RN1 and 17% of the injected RN1 had entered the nucleus. The diffusion rate through pores having a radius of 45 A was calculated for several possible molecular configurations of RN1. Using axial ratios of 34, 7.5, 2, and 1, the estimated times required to reach 63% of diffusion equilibrium are 757, 468, 6,940 h, and infinity, respectively. Even assuming an axial ratio of 7.5 (the most diffusive configuration) and an equilibrium distribution of 45, simple diffusion through the pores could account for only approximately 1/20 the observed nuclear uptake of RN1. This and other comparisons indicate that some form of mediated transport is involved in the nucleocytoplasmic exchange of this polypeptide.
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Selected References
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- De Robertis E. M., Longthorne R. F., Gurdon J. B. Intracellular migration of nuclear proteins in Xenopus oocytes. Nature. 1978 Mar 16;272(5650):254–256. doi: 10.1038/272254a0. [DOI] [PubMed] [Google Scholar]
- Feldherr C. M., Ogburn J. A. Mechanism for the selection of nuclear polypeptides in Xenopus oocytes. II. Two-dimensional gel analysis. J Cell Biol. 1980 Dec;87(3 Pt 1):589–593. doi: 10.1083/jcb.87.3.589. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Feldherr C. M., Pomerantz J. Mechanism for the selection of nuclear polypeptides in Xenopus oocytes. J Cell Biol. 1978 Jul;78(1):168–175. doi: 10.1083/jcb.78.1.168. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Feldherr C. M. The uptake of endogenous proteins by oocyte nuclei. Exp Cell Res. 1975 Jul;93(2):411–419. doi: 10.1016/0014-4827(75)90467-x. [DOI] [PubMed] [Google Scholar]
- Helenius A., Simons K. Solubilization of membranes by detergents. Biochim Biophys Acta. 1975 Mar 25;415(1):29–79. doi: 10.1016/0304-4157(75)90016-7. [DOI] [PubMed] [Google Scholar]
- Krohne G., Franke W. W. A major soluble acidic protein located in nuclei of diverse vertebrate species. Exp Cell Res. 1980 Sep;129(1):167–189. doi: 10.1016/0014-4827(80)90341-9. [DOI] [PubMed] [Google Scholar]
- Paine P. L., Feldherr C. M. Nucleocytoplasmic exchange of macromolecules. Exp Cell Res. 1972 Sep;74(1):81–98. doi: 10.1016/0014-4827(72)90483-1. [DOI] [PubMed] [Google Scholar]
- Paine P. L., Moore L. C., Horowitz S. B. Nuclear envelope permeability. Nature. 1975 Mar 13;254(5496):109–114. doi: 10.1038/254109a0. [DOI] [PubMed] [Google Scholar]
- Paine P. L., Scherr P. Drag coefficients for the movement of rigid spheres through liquid-filled cylindrical pores. Biophys J. 1975 Oct;15(10):1087–1091. doi: 10.1016/S0006-3495(75)85884-X. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Sabatini D. D., Kreibich G., Morimoto T., Adesnik M. Mechanisms for the incorporation of proteins in membranes and organelles. J Cell Biol. 1982 Jan;92(1):1–22. doi: 10.1083/jcb.92.1.1. [DOI] [PMC free article] [PubMed] [Google Scholar]