Kinesins are common in a variety of eukaryotic cells with diverse functions.A cDNA encoding a member of the Kinesin-14B subfamily is obtained using 3-RACE technology and named AtKP1 (for Arabidopsis kinesin protein 1).This cDNA has a maximum open reading frame of 3.3 kb encoding a polypeptide of 1087 aa.Protein domain analysis shows that AtKP1 contains the motor domain and the calponin homology domain in the central and amino-terminal regions,respectively.The carboxyl-terminal region with 202 aa residues is diverse from other known kinesins.Northern blot analysis shows that AtKP1 is widely expressed at a higher level in seedlings than in mature plants.2808 bp of the AtKP1 promoter region is cloned and fused to GUS.GUS expression driven by the AtKP1 promoter region shows that AtKP1 is mainly expressed in vasculature of young organs and young leaf trichomes,indicating that AtKP1 may participate in the differentiation or development of Arabidopsis thaliana vascular bundles and trichomes.A truncated AtKP1 protein containing the putative motor domain is expressed in E.coll and affinity-purified.In vitro characterizations indicate that the polypeptide has nucleotide-dependent microtubule-binding ability and microtubule-stimulated ATPase activity.