Genetic analysis of the regulation of the voltage-gated calcium channel homolog Cch1 by the γ subunit homolog Ecm7 and cortical ER protein Scs2 in yeast

The yeast Cch1/Mid1 Ca(2+) channel is equivalent to animal voltage-gated Ca(2+) channels and activated in cells incubated in low Ca(2+) medium. We herein investigated the third subunit, Ecm7, under the same cell culture conditions. The deletion of ECM7 slightly lowered Ca(2+) influx activity in the CNB1(+) background, in which calcineurin potentially dephosphorylates Cch1, but markedly lowered this activity in the cnb1Δ background. The deletion of the C-terminal cytoplasmic region of Ecm7 also reduced Ca(2+) influx activity. We identified a novel Cch1-interacting protein, Scs2, which is known as a cortical endoplasmic reticulum membrane protein. The deletion of SCS2 did not affect Ca(2+) influx activity when calcineurin was inhibited by FK506, but enhanced this activity by 35% when the enzyme was not inhibited. However, this enhancement was canceled by the deletion of ECM7. These results suggest that Cch1/Mid1 is regulated differentially by Ecm7 and Scs2 in a manner that is dependent on the phosphorylation status of Cch1.