Speaker: Dr. Kazuya Jibiki, Department of Life Science College of Humanities and Science, Nihon University

Title: A novel function of the nuclear transport factor importin α as a direct DNA-binding protein

Abstract: The nucleus of a eukaryotic cell is separated from the cytoplasm by the nuclear envelope, and large molecules such as proteins are transported in and out of the nucleus by transport receptors. importin α is a typical nuclear import receptor which transport hundreds of functional proteins into the nucleus. Human cells have seven family members of importin α genes that have cargo specificities, and these family members are differentially expressed depending on the tissue type. Meanwhile, various non-transport functions of importin α have been reported. Therefore, a multifaceted perspective is necessary to understand the role of importin α in cellular activities. We recently discovered that importin α directly binds DNA and revealed the unique binding property. Importin α binds multiple DNA sequences with different affinities, and efficiently slides along DNA. Surprisingly, importin α interacts simultaneously with cargo proteins and DNA, suggesting that importin α plays a role not only in nuclear import but also in the functional regulation of cargo proteins on DNA. Interestingly, the DNA binding domain of importin α is a chameleon sequence that changes its structure depending on the environments and it regulates each step of nuclear transport function of importin α by interacting with several molecules. We will review the nuclear transport function of importin α and present our recent findings on the function of DNA binding. We will also review the function and properties of the chameleon sequence of importin α and propose a new model of chromatin regulation focusing on the crosstalk between nuclear transport and DNA binding.