The noncoordinate expression of muscle-specific proteins in mutant rat skeletal myoblasts and reinitiation of differentiation in hybrids.

In rat skeletal myoblasts which are resistant to 5-azacytidine and fusion-incompetent, the muscle-specific protein, creatine phosphokinase, is produced but muscle-specific myosin is not. In human diploid fibroblast X rat myoblast hybrids, myoblast-specific properties are extinguished. Clones can be selected from the hybrids after a number of doublings which reexpress fusion but do not produce creatine phosphokinase. The conclusion is drawn that the expression of muscle-specific phenotype is not coordinate and fusion of myoblasts is not an essential requirement for the appearance of myoblast-specific proteins.