A positive screening for drugs that specifically inhibit the Ca2+ - Signaling activity on the basis of the growth promoting effect on a yeast mutant with a peculiar phenotype

An inappropriate activation of a signaling pathway in yeast often has a del eterious physiological effect and causes various defects, including growth defects. In a certain genetic background (Delta zds1) of Saccharomyces cere visiae, the cell-cycle progression in G2 is specifically blocked in the med ium with CaCl2 by the hyperactivation of the Ca2+-signaling pathways. Here, we developed a novel drug screening procedure designed to detect the activ e compounds that specifically attenuate the Ca2+-signaling activity on the basis of the ability to abrogate the growth defect of the cells suffering f rom the hyperactivated Ca2+ signal. Using known calcineurin inhibitors as m odel compounds, we have established the screening conditions for the drugs that suppress the Ca2+-induced growth inhibition. An indicator strain with an increased drug sensitivity was constructed with a syr1/erg3 null mutatio n.