Plays a role in mediating store-operated Ca(2+) entry (SOCE), a Ca(2+) influx following depletion of intracellular Ca(2+) stores. Functions as a highly sensitive Ca(2+) sensor in the endoplasmic reticulum which activates both store-operated and store-independent Ca(2+)-influx. Regulates basal cytosolic and endoplasmic reticulum Ca(2+) concentrations. Upon mild variations of the endoplasmic reticulum Ca(2+) concentration, translocates from the endoplasmic reticulum to the plasma membrane where it probably activates the Ca(2+) release-activated Ca(2+) (CRAC) channels ORAI1, ORAI2 and ORAI3. May inhibit STIM1-mediated Ca(2+) influx. Oligomer with STIM1. Interacts with ORAI1. Dynamically translocates from a uniform endoplasmic reticulum distribution to punctual endoplasmic reticulum-plasma membrane junctions in response to decrease in endoplasmic reticulum Ca(2+) concentration. Expressed in all tissues and tumor cell lines examined. Glycosylated. Phosphorylated predominantly on Ser residues. Unusual initiator. The initiator methionine is coded by a non-canonical CTG leucine codon. Truncated N-terminus. Probable cloning artifact. Unusual initiator. The initiator methionine is coded by a non-canonical CTG leucine codon.