Association of a Mr 50,000 cap-binding protein with the cytoskeleton in baby hamster kidney cells.

A monoclonal antibody directed against eukaryotic mRNA 5'-cap-binding protein (anti-CBP antibody) was used to localize cap-binding protein (CBP) in BHK-21 baby hamster kidney cells by immunofluorescence microscopy. It was found that the antibody reacts with a fibrous network extending through the cytoplasm in a radial arrangement. The network behaves like intermediate filaments in colchicine-treated cells, suggesting a direct or indirect linkage of CBP with intermediate filaments. The association of CBP with a cytoskeletal element was further confirmed by isolation of proteins from Triton X-100-extracted cells and identification of CBP in the cytoskeletal fraction with anti-CBP antibody. The major polypeptide reacting with anti-CBP antibody is a Mr 50,000 component. Tryptic peptide mapping showed that this polypeptide is related to a Mr 24,000 polypeptide identified as CBP in earlier experiments [Sonenberg, N., Morgan, M. A., Testa, D., Colonna, R. J. & Shatkin, A. J. (1978) Proc. Natl. Acad. Sci. USA 75, 4843-4847].