IMMUNOLOCALIZATION OF THE EXOCYTOSIS-SENSITIVE PHOSPHOPROTEIN, PP63 PARAFUSIN, IN PARAMECIUM CELLS USING ANTIBODIES AGAINST RECOMBINANT PROTEIN/

We have localized a structure-bound fraction of the exocytosis-sensiti ve phosphoprotein, PP63/parafusin (PP63/pf), in Paramecium cells by wi dely different methods. We combined cell fractionation, western blots, as well as light and electron microscopy (pre- and postembedding immu nolabeling), applying antibodies against the recombinant protein. PP63 /pf is considerably enriched in certain cortical structures, notably t he outlines of regular surface fields (kinetids), docking sites of sec retory organelles (trichocysts) and the membranes of subplasmalemmal C a2(+)-stores (alveolar sacs). From our localization studies we tentati vely derive several potential functions for PP63/pf, including cell su rface structuring, assembly of exocytosis sites, and/or Ca2(+) homeost asis.