We cloned a cDNA encoding caltractin, a 20 kDa calcium-binding protein, from Dunaliella salina (DSCALT). The Ca(2+)-bound mobility shift detected in Chlamydomonas caltractin was hardly detectable in DSCALT. Also, some differences were found in the electrophoretic mobility between the native DSCALT and the bacterial-expressed DSCALT. This difference may have resulted from the posttranslational modification. Immunoblot analysis revealed that this protein might be localized mainly in the basal body complex, the major microtubule organizing center (MTOC) in D.salina and the functional homologue of the centrosome of the animal cell.