Figure 4.

Nuclear import of NP-importin α- and β-coated gold particles into Xenopus oocyte nuclei. NP-coated gold particles with diameter of 26 ± 3 nm were incubated in vitro first with importin α and then with importin β. The resulting complexes were injected into the cytoplasm of Xenopus oocytes and their nuclear import was followed by electron microscopy. Shown are low- (A) and high (B)-magnification views of nuclear envelope cross sections with adjacent cytoplasm (c) and nucleoplasm (n). Arrowheads point to gold particles that reached the nucleus or are associated with the nuclear face of the NPC. Gold particles as large as 26 nm in diameter (without the protein coat) were able to cross the nuclear pores and enter the nucleus of Xenopus oocytes. Shown is also a gallery of gold particles that were found in the nucleus of Xenopus oocytes. Bars, 200 nm (A) and 50 nm (B).