Modulators of Nuclear Localization of the Human Enzyme ADAR1

The RNA editing enzyme hsADAR1 (human adenosine deaminase that acts on RNA 1) converts adenosines to inosines in double-stranded RNA and is a transcription-dependent shuttling protein. To enter the nucleus ADAR1 contains an atypical nuclear localization signal (NLS) overlapping the third double-stranded RNA binding domain (dsRBD) in the center of the enzyme. This study is concentrating on the characterization of the roles of dsRBD1 and 3 in the shuttling behavior of the enzyme. On the one hand our results indicate that NLS comprising residues are spread throughout the entire dsRBD. Additionally, several karyopherins were tested whether they can interact with dsRBD3 and mediate nuclear import of hsADAR1. Recent data revealed Transportin-1 as the most probable candidate. On the other hand to elucidate the mechanism that interferes with nuclear accumulation of hsADAR1, experiments were focused on Exportin-5, a karyopherin exporting dsRBDs and micro RNAs. Although the export factor binds ADAR1's dsRBDs in a RNA- and RanGTP dependent manner in vitro, cell based assays fail to confirm an involvement of Exportin-5 in the export of ADAR1.