Whose Finger Is on the Switch?

David S. Goldfarb Proteins and nucleic acids are transported into and out of the cell nucleus through nuclear pores. In his Perspective, Goldfarb discusses two reports in this issue in which a central control switch in nuclear transport is identified as Ran, a small guanosine triphosphatase. Not only is this molecule a key component in turning the import and export processes on and off ( Richards et al .), but it is also a target for vesicular stomatitis virus, which turns off nuclear traffic while co-opting the protein synthetic machinery in the cytoplasm ( Her et al .).