Monoclonal antibodies reveal structural similarity between cytoskeletal filaments and a model nucleopeptide

The cytoskeleton is considered to be a very important cellular component, playing a role in the interactions between different organelles. However, in many cases the true biochemical functions and some of the structural aspects of cytoskeletal filaments are still unknown. Several hybridoma cell lines producing monoclonal antibodies (Mab) against a complex of linear DNA with the tridecapeptide Dns-NH2-VVTGVKTGVKTVT-CO2H have been established. (Dns is 5-methylaminonaphthalene-1-sulphonic acid.) The organization of this complex, in which the DNA is in a compact form, has been well-characterized previously by physicochemical methods and electron microscopy. A monoclonal antibody, Mab 66/9, was selected for further study on the basis of its reactivity with the immunizing DNA-peptide complex and minimal reaction with DNA alone. In immunofluorescence studies with cultured cells, this Mab did not recognize any nuclear structures, but reacted with cytoskeletal intermediate filaments and with nuclear lamins. Thus, Mab 66/9 appears to define an epitope present in the immunizing DNA-peptide complex and in cytoskeletal elements. The epitope is probably determined by the conformation of the oligopeptide since it was not detected in denatured cell lysates. Our observations provide some indirect evidence in support of the DNA-binding properties of cytoskeletal components which have been hypothesized in some recent publications.