XVI International Botanical Congess

Most nuclear proteins contain a nuclear localization signal (NLS) and their import into the nucleus is initiated by recognition and binding to the NLS by importin alpha in the cytoplasm. We have cloned three importin alpha homologues from rice, importin alpha 1a, 1b and 2, respectively. Functional analyses show that recombinant proteins of all the three homologues bind functional NLS protein in vitro and, for rice importin alpha 1a and alpha 1b, also direct NLS proteins into the nucleus in a nuclear import assay system. RNA blot analysis revealed that they are differentially expressed in a tissue specific manner, and some ones are regulated negatively by light. These data show that they function as a component of NLS-receptor in plant cells, and suggest that each rice importin alpha may have distinct roles in the regulation of nuclear import of rice cells.