HOMOLOGS OF VERTEBRATE TYPE-I, TYPE-II AND TYPE-III INTERMEDIATE FILAMENT (IF) PROTEINS IN AN INVERTEBRATE - THE IF MULTIGENE FAMILY OF THECEPHALOCHORDATE BRANCHIOSTOMA

We searched for functional homologues of the four subfamilies of verte brate cytoplasmic intermediate filament (IF) proteins in the cephaloch ordate Branchiostoma. The epidermis contains in addition to IF protein s C2 and D1 two novel IF proteins E1 and E2. Both sequence comparisons as well as the obligatory heteropolymer formation by the recombinant proteins identify E1 as a type I keratin and E2 and D1 as type II kera tins, In contrast the non-epidermal B1 forms as type III homologue hom opolymeric IF. We propose that type I-III diversification of IF protei ns is a property of the chordate branch of metazoa and discuss a possi ble origin of type IV neurofilaments. (C) 1998 Federation of European Biochemical Societies.