Ultrastructural localization to 10 nm filaments of an insoluble 58K protein in cultured fibroblasts.

Using a simple procedure, we have isolated a Triton X-100 insoluble protein (58,000 mol wt) from cultured Chinese hamster ovary (CHO) cells, a fibroblastic cell line. The isolated protein, judged homogeneous by two-dimensional gel electrophoresis, was used to elicit antibodies in rabbits. The antiserum obtained is specific for the 58K protein as determined by immunoprecipitation from detergent solubilized 35S-labeled CHO cells and by antibody labeling of SDS solubilized Swiss 3T3 cell extracts separated on a 10% polyacrylamide gel. Indirect immunofluorescence localization with this antiserum in fixed permeabilized Swiss 3T3 cells, whose flat morphology makes them superior for localization studies, reveals filaments that radiate from the perinuclear region to the cell periphery. These filaments were identified as 10 nm filaments by electron microscopic localization using the EGS and ferritin bridge procedures. We conclude that the 58K protein is a major constituent of fibroblast 10 nm filaments. Other intracellular structures were not labeled by this technique.