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Nuclear Localization Signal Peptides Induce Molecular Delivery along Microtubules

Hanna Salman ^*, Asmahan Abu-Arish ^*, Shachar Oliel , Avraham Loyter , Joseph Klafter , Rony Granek  and Michael Elbaum ^*

^* Department of Materials and Interfaces, Weizmann Institute of Science, Rehovot 76100, Israel; Alexander Silberman Institute of Life Sciences, The Hebrew University of Jerusalem, Givat Ram, Jerusalem 91904, Israel; School of Chemistry, Tel Aviv University, Tel Aviv 69978, Israel; and Department of Biotechnology Engineering and The Institute for Applied Biosciences, Ben Gurion University of the Negev, Beer-Sheva 84105, Israel

Correspondence: Address reprint requests to Michael Elbaum, Tel.: 972-8-9343537; Fax: 972-8-9344138; E-mail: michael.elbaum{at}weizmann.ac.il.

Many essential processes in eukaryotic cells depend on regulated molecular exchange between its two major compartments, the cytoplasm and the nucleus. In general, nuclear import of macromolecular complexes is dependent on specific peptide signals and their recognition by receptors that mediate translocation through the nuclear pores. Here we address the question of how protein products bearing such nuclear localization signals arrive at the nuclear membrane before import, i.e., by simple diffusion or perhaps with assistance of cytoskeletal elements or cytoskeleton-associated motor proteins. Using direct single-particle tracking and detailed statistical analysis, we show that the presence of nuclear localization signals invokes active transport along microtubules in a cell-free Xenopus egg extract. Chemical and antibody inhibition of minus-end directed cytoplasmic dynein blocks this active movement. In the intact cell, where microtubules project radially from the centrosome, such an interaction would effectively deliver nuclear-targeted cargo to the nuclear envelope in preparation for import.