BINDING OF TFIID AND MEF2 TO THE TATA ELEMENT ACTIVATES TRANSCRIPTIONOF THE XENOPUS-MYODA PROMOTER

Members of the MyoD family of helix-loop-helix proteins control expres sion of the muscle phenotype by regulating the activity of subordinate genes. To investigate processes that control the expression of myogen ic factors and regulate the establishment and maintenance of the skele tal muscle phenotype, we have analyzed sequences necessary for transcr iption of the maternally expressed Xenopus MyoD (XMyoD) gene. A 3.5-kb DNA fragment containing the XMyoDa promoter was expressed in a somite -specific manner in injected frog embryos. The XMyoDa promoter was act ive in oocytes and cultured muscle cells but not in fibroblasts or non muscle cell lines. A 58-bp fragment containing the transcription initi ation site, a GC-rich region, and overlapping binding sites for the ge neral transcription factor TFIID and the muscle-specific factor MEF2 w as sufficient for muscle-specific transcription. Transcription of the minimal XMyoDa promoter in nonmuscle cells was activated by expression of Xenopus MEF2 (XMEF2) and required binding of both MEF2 and TFIID t o the TATA motif. These results demonstrate that the XMyoDa TATA motif is a target for a cell-type-specific regulatory factor and suggests t hat MEF2 stabilizes and amplifies XMyoDa transcription in mesodermal c ells committed to the muscle phenotype.