Slk19p is a centromere protein that functions to stabilize mitotic spindles

We have identified a novel centromere-associated gene product from Saccharo myces cerevisiae that plays a role in spindle assembly and stability. Strai ns with a deletion of SLK19 (synthetic lethal Kar3p gene) exhibit abnormall y short mitotic spindles, increased numbers of astral microtubules, and req uire the presence of the kinesin motor Kar3p for viability. When cells are deprived of both Slk19p and Kar3p, rapid spindle breakdown and mitotic arre st is observed. A functional fusion of Slk19p to green fluorescent protein (GFP) localizes to kinetochores and, during anaphase, to the spindle midzon e, whereas Kar3p-GFP was found at the nuclear side of the spindle pole body . Thus, these proteins seem to play overlapping roles in stabilizing spindl e structure while acting from opposite ends of the microtubules.