Kinesin is associated with a nonmicrotubule component of sea urchin mitotic spindles

Sea urchin embryos in second division have been lysed into microtubule-stabilizing buffers to yield mitotic cytoskeletons (MCSs) that consist of two mitotic spindles surrounded by a cortical array of filaments. Microtubules have been completely extracted from MCSs by incubation at 0 degrees C with Ca2+-containing buffer. An antibody to the microtubule translocator kinesin stains the spindles in MCSs and in MCSs treated with 5 mM ATP and also stains spindle-remnants of the MCSs after the microtubules have been extracted. We conclude that kinesin binds to a nonmicrotubule component in the mitotic spindle. Based on these results, we present several models of kinesin function in the spindle.