Yeast calmodulin localizes to sites of cell growth

Summary Intracellular localization of calmodulin was examined in the budding yeast,Saccharomyces cerevisiae. Distribution of calmodulin changes in a characteristic way during the cell cycle. Calmodulin localizes to a patch at the presumptive bud site of unbudded cells. It concentrates at the bud tip in small-budded cells, and later it diffuses throughout the entire bud. At cytokinesis, calmodulin is largely at the neck between the mother and daughter cells. Double staining experiments have shown that the location of some polarized actin dots is coincident with that of calmodulin dots. Polarized localization of actin dots is observed in cells depleted of calmodulin, suggesting that calmodulin is not required for localization of the actin dots. Thecdc24 mutant that has a defect in bud assembly at the restrictive temperature fails to exhibit polarized localization of calmodulin, indicating that theCDC24 gene product is responsible for controlling the polarity of calmodulin.