FIGURE 2 (a) Gels resulting from Western blot analysis of TFIID components (TAFs and TBP) involved in differentiation of myoblasts to myotubes in mouse muscle tissue. TFIID is represented by its component TBP; the TAF3-TRF3 complex is represented by TAF3. (b) A proposed model for cell differentiation from myoblast to myotube cells. A core transcription initiation complex including TAF3 and TRF3 functionally replaces the canonical TFIID complex in myotube cells, switching on the unique transcription pattern required during cell type–specific terminal differentiation.