Structure-function relationships of a yeast putative stretch-activated calcium channel

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1) The amino acid residue Phe^<356> of the putative stretch-activated Ca^<2+> channel Mid1 was determined to be important for cell viability in yeast. Systematic substitution of various amino acids for Phe^<355> revealed that hydrophobicity of this residue is critical.2) The Mid1 protein was found to be localized to the plasma membrane and endoplasmic reticulum membrane. Mid1 forms a oligomer via disulfide bonding.3) A multicopy suppressor of the mid1 mutation was isolated and characterized. This multicopy suppressor is an N-terminally truncated form of the Spa2 protein important for polarized morphgenesis.4) A gene encoding Cch1, which has been genetically suggested to function with Mid1 as a Ca^<2+> channel, was cloned. We have confirmed that Mid1 and Cch1 really cooperate to function as a Ca^<2+> channel.5) Rice OsTpc1 that is homologous to yeast Cch1 was found to be sensitive to blockers of L-type voltage-gated calcium channels. In addition, The Arabidopsis Mca1 protein, which can complement the lethality of the yeast mid1 mutant, was isolated and characterized. Mca1 is crucial for Ca^<2+> influx and touch sensing in primary roots.