MyoD muscle protein-DNA complex. Molecular model of the MyoD muscle protein (red and purple) bound to a strand of DNA (deoxyribonucleic acid, yellow and green). MyoD's role as a protein is to aid the regulation of muscle differentiation, the process where basic cell types become more specialised, in this case for muscle tissue. MyoD is an example of a basic helix-loop-helix (bHLH) transcription factor.