Mutations in SPC110, encoding the yeast spindle pole body calmodulin-binding protein, cause defects in cell integrity as well as spindle formation

The 110 kDa spindle pole body component, Spc110p, is an essential target of calmodulin in budding yeast. Cells with mutations which reduce calmodulin binding to Spc110p are unable to form a mitotic spindle and die. Here we sh ow that these effects can be overcome either directly by increasing extrace llular calcium or calmodulin expression, which reverse the primary spindle defect, or indirectly through increased extracellular osmolarity or high do sage of MID2 or SLG1/HCS77/ WSC1 which preserve viability. We propose that overcoming a cell integrity defect associated with the mitotic arrest enabl es the defective spindle pole bodies to provide sufficient function for pro liferation of a large proportion of mutant cells. Our findings demonstrate a role for calcium in the Spc110p-calmodulin interaction in vivo and have i mportant general implications for the interpretation of genetic interaction s involving cell integrity genes. (C) 2000 Elsevier Science B.V. All rights reserved.