The murine Nd1 gene encodes two forms of protein, Nd1-L and Nd1-S, both of which share the BTB/POZ domain, but Nd1-S lacks the kelch repeats. Although Nd1-L ubiquitously expresses, localizes in the cytoplasm and functions as a stabilizer of actin filaments, expression and function of Nd1-S were unknown. Here we show that Nd1-S were expressed in all tissues examined and localized in the nucleus as a speckled-like pattern. Furthermore, overexpression of Nd1-S perturbed cell growth of NIH3T3 cells at the G1/S phase of the cell cycle. These results suggest that Nd1-S may play a role in cell cycle progression in the nucleus.