THE ROLE OF THE CANNTG PROMOTER ELEMENT (E-BOX) AND THE MYOCYTE-ENHANCER-BINDING-FACTOR-2 (MEF-2) SITE IN THE TRANSCRIPTIONAL REGULATION OF THE CHICK MYOGENIN GENE

We have carried out an analysis of 833 bp of the chick myogenin gene 5' flanking sequence. A 131-bp segment of this upstream region, which contains a CANNTG promoter element (E box) and a myocyte-enhancer-binding-factor-2 (MEF-2) site, acts as a full promoter. It resembles the human and the mouse myogenin promoters in the structure and disposition of regulatory elements, including a TATA box and the transcription start site. Examination of eight myogenic factor/E protein combinations cotransfected with several myogenin promoter constructs into HeLa cells, reveals that the chick myogenin/E2-5 combination maximally activates the myogenin promoter. This activation is mediated through the E box motif; the MEF-2 site limits the factor combinations that can activate the myogenin promoter and enhances activation by myogenin/E2-5. We have found previously that activation of protein kinase C inactivates the transcription of the chick myogenin gene [Huang, C.-F, Neville, C. M. & Schmidt, J. (1993) Control of myogenic factor genes by the membrane depolarization/protein kinase C cascade in chick skeletal muscle, FEES Lett. 319, 21-25]. In this study, we show that the activation of protein kinase C inhibits the factor bound to the E box, which thereupon negatively regulates the activity of the MEF-2 binding protein.