Among cytoskeletal systems, the intermediate filaments (IFs)1 are unique because they are composed of different proteins in different tissues. These proteins share a common tripartite structure composed of an NH2-terminal head domain, a coiled-coil rod domain, and a COOH terminus of varying length. They are subdivided into six IF classes according to their amino acid sequence similarity (for review see Julien and Grosveld, 1991) and to the intron structure of their genomic sequences. Neurofilaments (NFs) are enriched in neurons, especially in large-caliber axons. They belong to the fourth group of IFs, which comprises three subunit proteins: NF-L (apparent molecular mass ∼68 kD), NF-M (idem. ∼160 kD), and NF-H (idem. ∼200 kD) (Hoffman and Lasek, 1975; Liem et al., 1978).
Neurofilaments in nerve axons are composed of a parallel array of 10-nm filaments with frequent crossbridges between NFs or between NFs and...
