Store-operated Ca2+ entry (SOCE) is a physiologically important process that is triggered by intracellular Ca2+ depletion. Recently, human Orai1 (the channel-forming subunit) and STIM1 (the calcium sensor) were identified as essential molecules for SOCE. Here, we report the cloning and functional analysis of three murine orthologs of Orai1, termed Orail, 2, and 3. Among the genes identified, Orail contains a distinctive proline- and arginine-rich N-terminal cytoplasmic sequence. Co-expression of STIM1 with Orail produced a marked effect on SOCE, while co-expression with Orai2 or Orai3 had little effect. Expression of Orail without its N-terminal tail had a marginal effect on SOCE, while chimeric Orai2 containing the Orai1 N-terminus produced a marked increase in SOCE. In addition, a truncated version of Orai1 containing the N-terminus without the pore-forming transmembrane domain had a dominant negative effect on SOCE. These results reveal the essential role of Orai1 and its N-terminal sequence in SOCE. (c) 2007 Elsevier Inc. All rights reserved.