Movie of C143S mutant Orai1-GCaMP6s and STIM1-mRFP expressed in Orai1 triple knockout HEK293 cells acquired by TIRF microscopy (related to Fig. 4A). TIRF images were acquired every 10 seconds for 16 minutes. The time frame of the movie is accelerated 10-fold. The fluorescence of Orai1-GCaMP6s is calcium sensitive.