TFIID (TBP) stabilizes the binding of MyoD to its DNA site at the promoter and MyoD facilitates the association of TFIIB with the preinitiation complex.

The myogenic determination factor MyoD activates the transcription of muscle-specific genes by binding to consensus DNA sites found in the regulatory sequences of these genes. The interaction of MyoD with the basal transcription machinery is not known. Several activators induce transcription by recruiting TFIID and/or TFIIB to the promoter. We asked whether MyoD interacted functionally with TFIID and TFIIB in transcription. We reconstituted in vitro DNA binding and transcription systems of MyoD and basal transcription factors, and found that MyoD function in transcription occurred during the assembly of the preinitiation complex. Interestingly, MyoD activated transcription without affecting the binding of TFIID to the promoter. However, TFIID or TBP dramatically stabilized the binding of MyoD to its recognition site. MyoD and TBP interacted in solution. Deletion analysis of MyoD suggested that interaction of MyoD with TBP is needed for its activity in transcription. At a later stage of assembly, MyoD stabilized the binding of TFIIB to the preinitiation complex. These findings suggest that MyoD is involved in two steps of preinitiation; first, TFIID stabilizes MyoD binding to its DNA recognition site and at a later stage MyoD facilitates the association of TFIIB with the preinitiation complex.