UASp regulatory sequences drive expression of Stim isoform A coding sequence (cloned from the LD45776 cDNA), tagged at the C-terminal end with EGFP. Mutations have been introduced into residues in the EF hand domain that are required for Ca[2+] binding (amino acid substitutions D155A and D157A); this has previously been shown to lock the Stim protein into an extended conformation that enables it to interact with Orai Ca[2+] influx channels specifically at endoplasmic reticulum-plasma membrane contact sites.