Yeast Dam1p Is Required to Maintain Spindle Integrity during Mitosis and Interacts with the Mps1p Kinase

We have identified a mutant allele of the DAM1 gene in a screen for mutations that are lethal in combination with the mps1-1 mutation. MPS1 encodes an essential protein kinase that is required for duplication of the spindle pole body and for the spindle assembly checkpoint. Mutations in six different genes were found to be lethal in combination with mps1-1, of which only DAM1 was novel. The remaining genes encode a checkpoint protein, Bub1p, and four chaperone proteins, Sti1p, Hsc82p, Cdc37p, and Ydj1p. DAM1 is an essential gene that encodes a protein recently described as a member of a microtubule binding complex. We report here that cells harboring the dam1-1 mutation fail to maintain spindle integrity during anaphase at the restrictive temperature. Consistent with this phenotype, DAM1 displays genetic interactions with STU1, CIN8, and KAR3, genes encoding proteins involved in spindle function. We have observed that a Dam1p-Myc fusion protein expressed at endogenous levels and localized by immunofluorescence microscopy, appears to be evenly distributed along short mitotic spindles but is found at the spindle poles at later times in mitosis.