Calreticulins, such as CALR3
, are Ca(2+)-binding chaperones localized mainly in the endoplasmic/sarcoplasmic reticulum Persson et al. (2002).
Using database analysis to identify CALR-like sequences, Persson et al. (2002) identified mouse and human CALR3, which they designated CRT2. The deduced proteins contain 380 and 384 amino acids, respectively. CALR3 has an N-terminal endoplasmic reticulum (ER) signal sequence, followed by a globular N domain, 2 Ca(2+)-binding domains, a P domain, and a C domain, and it ends with an ER-retention motif (RNEL). The N-terminal region also contains 3 conserved cysteines. Northern blot analysis of several human tissues detected a 1.3-kb CALR3 transcript only in testis.