Intermediate filaments from Chinese hamster ovary cells contain a single protein. Comparison with more complex systems from baby hamster kidney and mouse epidermal cells.

Intermediate filaments (IF) were prepared under identical conditions from Chinese hamster ovary (CHO), baby hamster kidney (BHK), and primary mouse epidermal cells. CHO and BHK cells each have a major IF protein (Mr = 55,000); these proteins comigrate on two-dimensional gels. BHK cells have an additional protein constituent (Mr = 54,000) which is absent from CHO. The IF preparation from the epidermal cells was considerably more complex, containing at least five proteins with molecular weights between 50,000 and 70,000, none of which has a mobility similar to the CHO protein. If assembled in vitro from crude CHO IF preparations were morphologically indistinguishable from filaments assembled from other cell types. Analysis of these in vitro polymerized filaments from CHO cells using circular dichroism and wide angle x-ray diffraction revealed that the CHO filaments were structurally similar to filaments prepared from BHK or epidermal cells. The Mr = 55,000 proteins from CHO and BHK cells were found to have identical one- and two-dimensional peptide maps, demonstrating that their amino acid sequences must be very similar. These studies indicate that CHO cells possess the simplest system thus far described for studying the assembly of intermediate filaments.