Calmodulin kinase 2 genetically interacts with Rch1p to negatively regulate calcium import into Saccharomyces cerevisiae after extracellular calcium pulse

After a single extracellular 100 mM calcium pulse (final concentration), wild type S. cerevisiae exhibits a sharp peak in cytosolic calcium. The concentration drops rapidly in these cells as the calcium is sequestered away in the endoplasmic reticulum, Golgi, and vacuoles leaving resting cytosolic levels higher than their original state, followed by changes in gene expression. In cells lacking calmodulin kinase 2 (Cmk2p), a secondary rise in cytosolic calcium concentration is seen after extracellular calcium increases and the cytosolic calcium is subsequently sequestered. Utilizing double deletions, we demonstrate that Cmk2p is modulating the activity of Rch1p, a known inhibitor of Channel X which is a yeast plasma membrane channel through which calcium ions are transported after an extracellular calcium pulse. We hypothesize that Cmk2p is acting as a regulator of Channel X by activating Rch1p and without CMK2, Channel X inactivation does not occur fully.