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▪ Abstract Calmodulin, a small, ubiquitous Ca<sup>2+</sup>-binding protein, regulates a wide variety of proteins and processes in all eukaryotes. CMD1, the single gene encoding calmodulin in S. cerevisiae, is essential, and this review discusses studies that identified many of calmodulin's physiological targets and their functions in yeast cells. Calmodulin performs essential roles in mitosis, through its regulation of Nuf1p/Spc110p, a component of the spindle pole body, and in bud growth, by binding Myo2p, an unconventional class V myosin required for polarized secretion. Surprisingly, mutant calmodulins that fail to bind Ca<sup>2+</sup> can perform these essential functions. Calmodulin is also required for endocytosis in yeast and participates in Ca<sup>2+</sup>-dependent, stress-activated signaling pathways through its regulation of a protein phosphatase, calcineurin, and the protein kinases, Cmk1p and Cmk2p. Thus, calmodulin performs important physiological functions in yeast cells in both its Ca<sup>2+</sup>-bound and Ca<sup>2+</sup>-free form. |
