The purpose of this project is to analyze the mechanisms which control the synthesis of myosin during the differentiation of embryonic skeletal muscle in cell culture. The mechanistic relationships between regulation of myosin synthesis and the control of fusion and cell division will be examined by studying the initiation of myosin synthesis by myoblasts under conditions in which fusion and cell division are manipulated experimentally. In addition, the synthesis, processing, and stability of the myosin messenger RNA will be examined in relation to the regulation of myosin synthesis during myogenesis. The purpose of these experiments is to determine whether myosin synthesis is controlled by the regulation of the transcription of the myosin genes of alternatively by post-transcriptional mechanisms which modulate the processing, the translation or the stability of myosin messenger RNA.