Binding of MyoR/E12 heterodimers to DNA. E12, MyoR, and/or myogenin were transcribed and translated separately or together, as indicated, using a coupled in vitro transcription/translation system. In vitro translation products were used in gel mobility-shift assays with an end-labeled double-stranded oligonucleotide probe corresponding to the MCK right E-box. In the presence of lysate alone, no binding activity was observed.