Kinesin is a microtubule-based motor protein with various functions related to the cell growth and division. It has been reported that Krp1p, kinesin-related protein 1, which belongs to the kinesin heavy chain superfamily, localizes on microtubules and may play an important role in cytokinesis. However, the function of Krp1p hits not been fully elucidated. In this study, we overexpressed an intact form and three different mutant forms of Krp1p in fission yeast Constructed by site-directed mutagenesis in two ATP-binding motifs or by truncation of the leucine zipper-like motif (LZiP). We observed hyper-extended microtubules and the aberrant nuclear shape in Krp1p-overexpressed fission yeast. As a functional consequence, a point mutation of ATP-binding domain 1 (G89E) in Krp1p reversed the effect of Krp1p overexpression in fission yeast. whereas the specific mutation in ATP-binding domain 2 (G238E) resulted in the altered cell polarity. Additionally. truncation of the leucine zipper-like domain (LZiP) at the C-terminal of Krp1p showed a normal nuclear division. Taken together, we Suggest that krp1p is involved in regulation of cell-polarized growth through ATP-binding motifs in fission yeast. © 2005 Elsevier Inc. All rights reserved.