[Actomyosin from a low-differentiation skeletal muscle tumor].

Actin and subunits of myosin were identified in actomyosin preparations isolated from a low-differentiated rhabdomyosarcoma. Determination was made of Ca2+-ATPase activity and of the ratio of concentrations of tumor myosin light chains. Aggregates were obtained bearing similarity with synthetic filaments. The tumor myosin has all the light chains characteristic of the myosin of definitive fast skeletal muscles, and does not have light chains corresponding to any other myosin isoforms. Quantitative peculiarities of light chain composition of tumor myosin may be explained by peculiarities of cell composition of the tumor. The data obtained indicate that the mechanism coordinating myosin gene expression is extremely resistant to tumoral discoordinating factors. Peculiarities of coordination of the expression of genes coding tissue-specific polypeptides are discussed.