Transcriptional activator which binds specifically to the MEF2 element, 5'-YTA[AT](4)TAR-3', found in numerous muscle-specific genes. Activates transcription via this element. May be involved in muscle-specific and/or growth factor-related transcription. Heterodimer. Interacts with HDAC9 (By similarity). Interacts with HDAC7. Highest expression found in embryonic heart and skeletal muscle. Low levels found in adult spleen, lung and testis while no expression is found in adult heart, brain or skeletal muscle. Higher expression in early embryo than in adult. Belongs to the MEF2 family.