Transcriptional activation domain of the muscle-specific gene-regulatory protein myf5

The muscle determination factor myf5 and other members of the family of skeletal muscle-specific regulatory proteins (MyoD), contains a highly conserved putative helix-loop-helix domain. In MyoD this motif is required for the initiation of myogenesis in C3H mouse 10T1/2 fibroblasts and other nonmuscle cells as well as for transcriptional activation of muscle genes. High affinity DNA binding of MyoD to regulatory DNA elements in muscle genes requires the formation of heterodimers with ubiquitous helix-loop-helix proteins such as E12 or E47. To investigate the potential of myf5 as a transcription factor, we have fused the GAL4 DNA-binding domain to various parts of myf5 protein and analysed the transactivation of a GAL4 reporter plasmid. Here we report that myf5 contains an intrinsic transcriptional activation domain which is distinct from the helix-loop-helix motif. The predominant transactivating effect is associated with the C-terminal half of the myf5 molecule. High-affinity sequence specific DNA binding of myf5 also requires hetero-oligomeric association with the enhancering protein E12 to confer muscle specific transactivation.