The function of ORAI1 (ORAI calcium release-activated calcium modulator 1, Ensembl gene identifier ENSG00000276045) is as follows. Pore-forming subunit of two major inward rectifying Ca(2+) channels at the plasma membrane: Ca(2+) release-activated Ca(2+) (CRAC) channels and arachidonate-regulated Ca(2+)-selective (ARC) channels (Probable) (PubMed:16645049, PubMed:16733527, PubMed:16807233, PubMed:16921383, PubMed:19249086, PubMed:19706554, PubMed:23307288, PubMed:26956484, PubMed:28219928). Assembles with ORAI2 and ORAI3 to form hexameric CRAC channels that mediate Ca(2+) influx upon depletion of endoplasmic reticulum Ca(2+) store and channel activation by Ca(2+) sensor STIM1, a process known as store-operated Ca(2+) entry (SOCE). Various pore subunit combinations may account for distinct CRAC channel spatiotemporal and cell-type specific dynamics. ORAI1 mainly contributes to the generation of Ca(2+) plateaus involved in sustained Ca(2+) entry and is dispensable for cytosolic Ca(2+) oscillations, whereas ORAI2 and ORAI3 generate oscillatory patterns. CRAC channels assemble in Ca(2+) signaling microdomains where Ca(2+) influx is coupled to calmodulin and calcineurin signaling and activation of NFAT transcription factors recruited to ORAI1 via AKAP5. Activates NFATC2/NFAT1 and NFATC3/NFAT4-mediated transcriptional responses. CRAC channels are the main pathway for Ca(2+) influx in T cells and promote the immune response to pathogens by activating NFAT-dependent cytokine and chemokine transcription (PubMed:16582901, PubMed:17442569, PubMed:19182790, PubMed:20354224, PubMed:22641696, PubMed:26221052, PubMed:32415068, PubMed:33941685). Assembles with ORAI3 to form channels that mediate store-independent Ca(2+) influx in response to inflammatory metabolites arachidonate or its derivative leukotriene C4, termed ARC and LRC channels respectively (PubMed:19622606, PubMed:32415068). Plays a prominent role in Ca(2+) influx at the basolateral membrane of mammary epithelial cells independently of the Ca(2+) content of endoplasmic reticulum or Golgi stores. May mediate transepithelial transport of large quantities of Ca(2+) for milk secretion (By similarity) (PubMed:20887894). {ECO:0000250|UniProtKB:Q8BWG9, ECO:0000269|PubMed:16582901, ECO:0000269|PubMed:16645049, ECO:0000269|PubMed:16733527, ECO:0000269|PubMed:16807233, ECO:0000269|PubMed:16921383, ECO:0000269|PubMed:17442569, ECO:0000269|PubMed:19182790, ECO:0000269|PubMed:19249086, ECO:0000269|PubMed:19622606, ECO:0000269|PubMed:19706554, ECO:0000269|PubMed:20354224, ECO:0000269|PubMed:20887894, ECO:0000269|PubMed:22641696, ECO:0000269|PubMed:23307288, ECO:0000269|PubMed:26221052, ECO:0000269|PubMed:26956484, ECO:0000269|PubMed:28219928, ECO:0000269|PubMed:32415068, ECO:0000269|PubMed:33941685, ECO:0000305|PubMed:16766533}. [Isoform alpha]: Pore-forming subunit of both CRAC and ARC channels. Couples Ca(2+) influx to NFAT-mediated transcriptional responses. {ECO:0000269|PubMed:16921383, ECO:0000269|PubMed:17442569, ECO:0000269|PubMed:19182790, ECO:0000269|PubMed:19249086, ECO:0000269|PubMed:19622606, ECO:0000269|PubMed:19706554, ECO:0000269|PubMed:22641696, ECO:0000269|PubMed:26221052, ECO:0000269|PubMed:33941685}. [Isoform beta]: Pore-forming subunit of CRAC channels exclusively. {ECO:0000269|PubMed:22641696, ECO:0000269|PubMed:26221052, ECO:0000269|PubMed:33941685}.