THE MAIZE ABSCISIC ACID-RESPONSIVE PROTEIN RAB17 IS LOCATED IN THE NUCLEUS AND INTERACTS WITH NUCLEAR-LOCALIZATION SIGNALS

The maize abscisic acid (ABA)-responsive rab17 mRNA and Rab17 protein distribution in maize embryo tissues was investigated by in situ hybri dization and immunocytochemistry. rab17 mRNA and Rab17 protein were fo und in all cells of embryo tissues. Synthesis of rab17 mRNA occurred i nitially in the embryo axis. As maturation progressed, rab17 mRNA was detectable in the scutellum and accumulated in axis cells and provascu lar tissues. However, the response to exogenous ABA differed in variou s embryo cell types. The Rab17 protein was located in the nucleus and in the cytoplasm, and qualitative differences in the phosphorylation s tates of the protein were found between the two subcellular compartmen ts. Based on the similar domain arrangements of Rab17 and a nuclear lo calization signal (NLS) binding phosphoprotein, Nopp140, interaction o f Rab17 with NLS peptides was studied. We found specific binding of Ra b17 to the wild-type NLS of the SV40 T antigen but not to an import in competent mutant peptide. Moreover, binding of the NLS peptide to Rab1 7 was found to be dependent upon phosphorylation. These results sugges t that Rab17 may play a role in nuclear protein transport.