A NEW TETRAHYMENA ACTIN-BINDING PROTEIN IS LOCALIZED IN THE DIVISION FURROW

Using an F-actin affinity column, a 60 kDa fragment of a 71 kDa F-acti n-binding protein was partially purified from Tetrahymena pyriformis, After digestion of the 60 kDa fragment with cyanogen bromide, the N-te rminal 21-amino acid sequence of one of the resulting peptides was fou nd to show sequence similarity to a region near the actin-binding site (amino acid residues 260-281) of yeast fimbrin, An antibody prepared against a synthesized 21-mer oligopeptide reacted with the 71 kDa prot eins in T. pyriformis and T. thermophila cell extracts, suggesting tha t the 60 kDa fragment was produced from the 71 kDa protein through par tial digestion occurring during isolation, The 60 kDa fragment bound t o Tetrahymena F-actin as well as to rabbit skeletal muscle F-actin, an d induced the bundling of Tetrahymena F-actin, Indirect immunofluoresc ence revealed colocalization of the 71 kDa protein and actin in the or al apparatus and the deep fiber bundles in T. pyriformis. On the other hand, in T. thermophila, the 71 kDa protein was localized in the oral apparatus and the contractile vacuole pores during the interphase, Du ring cytokinesis, the 71 kDa protein was localized in the division fur row, Therefore, the 71 kDa protein seems to associate with the actin c ytoskeleton, and to regulate the actin filament organization during ph agocytosis and cytokinesis in Tetrahymena.