Inhibition of in vitro Nuclear Transport by a Lectin That Binds to Nuclear Pores

• Published in: The Journal of cell biology 1987-02, Vol.104 (2), p.189-200
• Main Authors: Finlay, Deborah R., Newmeyer, Donald D., Price, Todd M., Forbes, Douglass J.
• Format: Article
• Language: English
• Subjects: Acetylglucosamine - pharmacology; Animals; Biological and medical sciences; Biological Transport - drug effects; Cell nucleus; Cell structures and functions; DNA; Female; Fluorescence; Fundamental and applied biological sciences. Psychology; Glycoproteins; Lectins; Lectins - pharmacology; Liver; Liver - metabolism; Molecular and cellular biology; Nuclear Envelope - drug effects; Nuclear Envelope - metabolism; Nuclear Envelope - ultrastructure; Nuclear membrane; Nuclear pore; Nuclear Proteins; Nucleoplasmins; Nucleoproteins - metabolism; Oocytes - physiology; Ova; Phosphoproteins; Rats; Spermatozoa; Tissue Extracts - pharmacology; Wheat Germ Agglutinins - pharmacology; Xenopus
• ISSN: 0021-9525; 1540-8140
• DOI: 10.1083/jcb.104.2.189

Selective transport of proteins is a major mechanism by which biochemical differences are maintained between the cytoplasm and nucleus. To begin to investigate the molecular mechanism of nuclear transport, we used an in vitro transport system composed of a Xenopus egg extract, rat liver nuclei, and a fluorescently labeled nuclear protein, nucleoplasmin. With this system, we screened for inhibitors of transport. We found that the lectin, wheat germ agglutinin (WGA), completely inhibits the nuclear transport of fluorescently labeled nucleoplasmin. No other lectin tested affected nuclear transport. The inhibition by WGA was not seen when N-acetylglucosamine was present and was reversible by subsequent addition of sugar. When rat liver nuclei that had been incubated with ferritin-labeled WGA were examined by electron microscopy, multiple molecules of WGA were found bound to the cytoplasmic face of each nuclear pore. Gel electrophoresis and nitrocellulose transfer identified one major and several minor nuclear protein bands as binding 125 I-labeled WGA. The most abundant protein of these, a 63-65-kD glycoprotein, is a candidate for the inhibitory site of action of WGA on nuclear protein transport. WGA is the first identified inhibitor of nuclear protein transport and interacts directly with the nuclear pore.