| Research Abstract |
Actin plays central roles in the organization and dynamics of the cytosketeton. Within a few decades of the first isolation of actin from muscle, it was shown that actin filaments form the main architecture of the cytoskeleton, and that the dynamics of the cytoskeleton are regulated by the assembly/disassembly of the filament. Because of these characteristics of actin, previous researchers hypothesized that actin and/or its evolutionarily related molecules were involved in the organization and dynamics of the nucleus. However, actin filaments were observed only in the cytoplasm, and no molecule evolutionarily related to actin was identified at the time. The hypothesis was therefore regarded with skepticism for a long time. When the subcellular localizations of the other yeast Arps were investigated, unexpectedly more than half of them, including Arp5, Arp6, Arp7, Arp8, and Arp9, were predominantly localized in the nucleus, and Arp1, Arp2, Arp3, and Arp10 were observed in the cytoplasm. This suggests that the roles of Arps in the nucleus are not less significant than those in the cytoplasm. We have also discovered Arps localized in the nucleus in mammals. One of the nuclear Arps, Arp6 of budding yeast was shown to be a component of Swr1 complex, which exchange histone H2A for its variant H2A.Z. We showed that Arp6 was present in chromatin regions adjacent to telomere, and was required for proper organization of heterochromatin and distribution of Sir3. We also showed that human hArp6 interacted with hTPR1, which shuttles between cell nucleus and the cytoplasm. The property of hTPR1 might be involved in the regulation of Arp6 function. We have partially purified complexes containing hArp6, and analyzed it. Apart of these researches were performed in the laboratory of Prof.Ulrike Wintersberger.
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