IMMUNOFLUORESCENCE LOCALIZATION OF A 23-KDA TETRAHYMENA CALCIUM-BINDING PROTEIN, TCBP-23, IN THE CELL CORTEX

Previously, we succeeded in cloning a cDNA of the 23-kDa Tetrahymena C a2+-binding protein, designated TCBP-23. Analysis of the deduced amino acid sequences showed that TCBP-23 is a member of the EF-hand family of Ca2+-binding proteins. However, its physiological function was not elucidated, In the studies reported here, recombinant TCBP-23 was expr essed in Escherichia coil and purified, Since recombinant TCBP-23 bind s Ca2+ in vitro, Ca2+-binding domains of the protein are likely to be functional in vivo. Rabbit antibodies against TCBP-23 were raised and used to determine the intracellular localization of the protein in Tet rahymena cells by indirect immunofluorescence, The antibodies strongly stained the whole cell cortex except for the oral apparatus and aroun d the basal bodies, TCBP-23 remained in detergent-extracted cells, sug gesting that it is associated with the epiplasm, the membrane skeleton of Tetrahymena. These results suggest that TCBP-23 may mediate Ca2+-r egulated processes in the cell cortex.