The intracellular localization, and thereby the function, of a number of key regulator proteins tagged with a short leucine-rich motif (the nuclear export signal or NES) is controlled by CRM1/exportin1, which is involved in the export of these proteins from the nucleus . A common characteristic of these regulators is their transient action in the nucleus during either a specific phase of the cell cycle or in response to specific signals . Here, we show that a particular member of the class II histone-deacetylases mHDA2/mHDAC6  belongs to this family of cellular regulators that are present predominantly in the cytoplasm, but are also capable of shuttling between the nucleus and the cytoplasm. A very potent NES present at the amino terminus of mHDAC6 was found to play an essential role in this shuttling process. The sub-cellular localization of mHDAC6 appeared to be controlled by specific signals, since the arrest of cell proliferation was found to be associated with the translocation of a fraction of the protein into the nucleus. Data presented here suggest that mHDAC6 might be the first member of a functionally distinct class of deacetylases, responsible for activities not shared by other known histone deacetylases.