Novel form of non-muscle tropomyosin in human fibroblasts.

The cytoskeletal extracts of cultured human fibroblasts were found to contain at least four distinct polypeptides, each of which demonstrated the resistance to denaturation and the acidic isoelectric point characteristic of tropomyosin. One of these, hscp 36 (heat-stable cytoskeletal protein having an apparent molecular weight of 36,000), cross-reacted efficiently with an antiserum to chicken skeletal muscle tropomyosin. Furthermore, the messenger RNA coding for hscp 36 was selected by a chicken complementary DNA clone containing a tropomyosin sequence. The abundance of mRNA coding for hscp 36 was found to be similar in both normal and simian virus 40 (SV40) transformed human fibroblasts. The apparent molecular weight of hscp 36 is different from non-muscle tropomyosins previously isolated from human sources, which show the apparent molecular weight of 30,000 normally associated with non-muscle tropomyosin. This, together with the complexity of the heat-stable cytoskeletal proteins present in human fibroblasts, suggests the existence of multiple genes coding for human non-muscle tropomyosins.