Tetrahymena elongation factor-1 alpha is localized with calmodulin in the division furrow

Translation elongation factor 1 alpha (EF-1 alpha) catalyzes the GTP-depend ent binding of aminoacyl-tRNA to ribosomes, We previously reported that Tet rahymena EF-1 alpha induced the formation of bundles of rabbit skeletal mus cle filamentous actin (F-actin) as well as Tetrahymena F-actin [Kurasawa et al. (1996) Zool, Sci, (Tokyo) 13, 371-375], and that Ca2+/calmodulin (CaM) regulated the F-actin-bundling activity of EF-1 alpha [Kurasawa ct al, (19 96) J, Biochem, 119, 791-798]. In the present study, we investigated the bi nding between Tetrahymena EF-1 alpha and CaM using a Tetrahymena EF-1 alpha affinity column, and the localization of EF-1 alpha and CaM by indirect im munofluorescence. Only CaM in the Tetrahymena cell extract bound to Tetrahy mena EF-1 alpha in a Ca2+-dependent manner. In interphase Tetrahymena cells , EF-1 alpha and CaM are colocalized in the crescent structure of the oral apparatus and the apical ring, while in dividing cells, they are colocalize d in the division furrow. This is the first report describing the coexisten ce of EF-1 alpha and CaM in the division furrow, suggesting that EF-1 alpha and CaM are involved in the organization of contractile ring microfilament s during cytokinesis.