The 68,000-Dalton Neurofilament-Associated Polypeptide is a Component of Nonneuronal Cells and of Skeletal Myofibrils
Purified preparations of 10-nm neurofilaments from rat spinal cord and bovine or porcine brain contain a predominant 68,000-dalton polypeptide. This polypeptide is also a major component of the neurofilaments that copurify with brain tubulin isolated by cycles of polymerization and depolymerization. A protein that has the same isoelectric point and molecular weight as the neurofilament-associated polypeptide has also been identified as a cytoskeletal protein in a variety of avian and mammalian cell types, including baby hamster kidney (BHK-21) mouse 3T3, Novikoff rat hepatoma, chicken fibroblast, and chicken muscle cells. This protein is also a component of isolated chicken skeletal myofibrils. One-dimensional peptide maps of the 68,000-dalton proteins purified by two-dimensional isoelectric focusing/NaDodSO4/polyacrylamide gel electrophoresis from myofibrils, cycled tubulin, purified neurofilaments, and various cultured cell types were identical. In immunofluorescence this protein was associated with cytoplasmic intermediate filaments and myofibril Z discs. These results indicate that the neurofilament-associated polypeptide is a conserved protein that is present in many different cell types in addition to neuronal cells. Because some of these cells contain the major components of two other intermediate filament classes, desmin and vimentin, a given cell type may contain the subunits of at least three distinct intermediate filament types.
Additional Information© 1980 by the National Academy of Sciences Communicated by James F. Bonner, December 10, 1979 We thank Dr. C. O'Connor and B. L. Granger for their helpful comments, J. Sauer for her help in the preparation of the manuscript, and I. Lielausis for her technical assistance. This work was supported by a grant from the National Institutes of Health (PHS GM 06965) and by a grant from the Muscular Dystrophy Association of America. The publication costs of this article were defrayed in part by page charge payment. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. §1734 solely to indicate this fact.
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