Background: STIM1 gates TRPC channels, but the interacting domains are unknown. Results: The TRPC N and C terminus coiled coil domains interact to restrict access of STIM1. Their dissociation by cell stimulation promotes STIM1 interaction. Conclusion: The STIM1 Orai1-activating region (SOAR) domain interacts with the TRPC C terminus CCD to open the channels. Significance: The findings reveal how STIM1 opens the TRPC channels to control receptor-stimulated Ca2+ influx.