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 mutatio ns that are lethal in combination with the mps1-1 mutation. MPS1 encodes an essential protein kinase that is required for duplication of the spindle p ole body and for the spindle assembly checkpoint. Mutations in six differen t genes were found to be lethal in combination with mps1-1, of which only D AM1 was novel. The remaining genes encode a checkpoint protein, Bub1p, and four chaperone proteins, Sti1p, Hsc82p, Cdc37p, and Ydj1p. DAM1 is an essen tial gene that encodes a protein recently described as a member of a microt ubule binding complex. We report here that cells harboring the dam1-1 mutat ion fail to maintain spindle integrity during anaphase at the restrictive t emperature. Consistent with this phenotype, DAM1 displays genetic interacti ons with STU1, CIN8, and KAR3, genes encoding proteins involved in spindle function. We have observed that a Dam1p-Myc fusion protein expressed at end ogenous levels and localized by immunofluorescence microscopy, appears to b e evenly distributed along short mitotic spindles but is found at the spind le poles at later times in mitosis.