Demonstration of actin in the protozoon--Gregarina

Actin was identified in the motile trophozoites of Gregarina by indirect immunofluorescence microscopy. Ultrastructurally actin was found by immunogold labelling to be associated with the internal cytomembranes of the ectoplasmic folds and the general ectoplasmic region below the folds. Western blotting with antibodies to actin identified polypeptides with molecular weights around 43kD and 98kD in non-ionic detergent extracted trophozoites. The possibility of two distinct forms of cytoplasmic actin (43kD and 98kD) was considered.