1. 1 The Cytokeratins as a Member of the Intermediate Filament Protein Family Intermediate filaments together with microtubules and actin microfilaments make up the filamentous cytoskeleton found in the cytoplasm of vertebrate cells. Recently, intermediate filament proteins have also been described in invertebrates, but their chemistry is not yet known (for review see Biessmann and Walter 1989). These filaments (about 10 nm in diameter) used to be categorized into five classes - cytokeratin, vimentin, desmin, glial fibrillary acidic protein (GFAP), and neurofilaments (NFs). The expression of...