Molecular characterization of the major membrane skeletal protein in the ciliate Tetrahymena pyriformis suggests n-plication of an early evolutionaryintermediate filament protein subdomain

Epiplasmin C is the major protein component of the membrane skeleton in the ciliate Tetrahymena pyriformis. Cloning and analysis of the gene encoding epiplasmin C showed this protein to be a previously unrecognized protein. I n particular, epiplasmin C was shown to lack the canonical features of alre ady known epiplasmic proteins in ciliates and flagellates. By means of hydr ophobic cluster analysis (HCA), it has been shown that epiplasmin C is cons tituted of a repeat of 25 domains of 40 residues each. These domains are re lated and can be grouped in two families called types I and types II, Conne ctions between types I and types II present rules that can be evidenced in the sequence itself, thus enforcing the validity of the splitting of the do mains, Using these repeated domains as queries, significant structural simi larities were demonstrated with an extra six heptads shared by nuclear lami ns and invertebrate cytoplasmic intermediate filament proteins and deleted in the cytoplasmic intermediate filament protein lineage at the protostome- deuterostome branching in the eukaryotic phylogenetic tree.