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

Abstract

THE human muscle determination factor myf5, like MyoD (ref. 1) and other members of the family of skeletal muscle-specific regulatory proteins^2–7, contains a highly conserved putative helix–loop–helix domain⁸. In MyoD this motif is required for the initiation of myogenesis in C3H mouse 10T1/2 fibroblasts⁹ and other non-muscle cells¹⁰ as well as for transcriptional activation of muscle genes. High affinity DNA binding of MyoD to regulatory DNA elements in muscle genes^11,12 requires the formation of heterodimers with ubiquitous helix–loop–helix proteins such as E12 or E47 (refs 13, 14). To investigate the potential of myf5 as a transcription factor, we have fused the GAL4 DNA-binding domain to various parts of the 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 trans-activating 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 enhancer-binding protein E12 to confer muscle-specific transactivation.