DSK1, A NOVEL KINESIN-RELATED PROTEIN FROM THE DIATOM CYLINDROTHECA-FUSIFORMIS THAT IS INVOLVED IN ANAPHASE SPINDLE ELONGATION

We have identified an 80-kD protein that is involved in mitotic spindl e elongation in the diatom Cylindrotheca fusiformis. DSK1 (Diatom Spin dle Kinesin 1) was isolated using a peptide antibody raised against a conserved region in the motor domain of the kinesin superfamily. By se quence homology, DSK1 belongs to the central motor family of kinesin-r elated proteins. Immunoblots using an antibody raised against a noncon served region of DSK1 show that DSK1 is greatly enriched in mitotic sp indle preparations. Anti-DSK1 stains the diatom central spindle with a bias toward the midzone, and staining is retained in the spindle midz one during spindle elongation in vitro. Furthermore, preincubation wit h anti-DSK1 blocks function in an in vitro spindle elongation assay. T his inhibition of spindle elongation can be rescued by preincubating c oncurrently with the fusion protein against which anti-DSK1 was raised . We conclude that DSK1 is involved in spindle elongation and is likel y to be responsible for pushing half-spindles apart in the spindle mid zone.