Identification of elongation factor-1α as a Ca²⁺/calmodulin-binding protein in Tetrahymena cilia

Calmodulin (CaM) is known to be a ciliary component. However, the function of CaM in cilia or flagella has not been well understood. Immunoelectron microscopy using anti-CaM antibody showed that CaM was localized on the axonemal microtubules (MTs) and matrix of Tetrahymena cilia. To investigate the signal transduction of Ca²⁺/CaM in cilia, we performed Ca²⁺/CaM-affinity column chromatography in the membrane and matrix fraction. Elongation factor-1α (EF-1α) was identified as a Ca²⁺/CaM-binding protein in cilia. EF-1α is a highly conserved protein and functions in protein translation. In addition, EF-1α has been reported to interact with MTs and F-actin in several organisms. Immunoelectron microscopy showed that EF-1α was localized on the axonemal MTs. However, in immunoblot analysis, EF-1α was mainly extracted in the membrane and matrix fraction from the axonemal MTs by 1% Triton X-100 extraction. These results suggest that interaction between EF-1α and axonemal MTs is weak and sensitive to treatment with 1% Triton X-100 and that EF-1α mediates between axonemal MTs and CaM in the presence of Ca²⁺. Moreover, EF-1α was also localized in cilia of Paramecium, suggesting that EF-1α functions as a target protein of Ca²⁺/CaM in ciliate cilia.