MyoD-E protein heterodimers interact with MEF2 proteins to synergistically activate myogenesis. This interaction occurs via association of these two heterologous classes of transcription factors through their DNA-binding and dimerization motifs. The combinatorial associations of these two protein families appear to establish a transcriptional code specific for skeletal muscle gene activation. Together with the Mef2 proteins and E proteins, MyoD transcription factors are responsible for coordinating muscle-specific gene expression in the undifferentiated myoblast. MyoD activation leads to expression of myogenin, M-cadherin, myosin heavy and light chains, and muscle creatine kinase.