Acts as a transcriptional activator that promotes transcription of muscle-specific target genes and plays a role in muscle differentiation. Together with MYF5 and MYOG, co-occupies muscle-specific gene promoter core region during myogenesis. Induces fibroblasts to differentiate into myoblasts. Interacts with and is inhibited by the twist protein. This interaction probably involves the basic domains of both proteins (By similarity). Efficient DNA binding requires dimerization with another bHLH protein. Seems to form active heterodimers with ITF-2. Interacts with SUV39H1. Interacts with DDX5. Interacts with CHD2. Interacts with TSC22D3 (By similarity). Interacts with SETD3 (By similarity). Interacts with P-TEFB complex; promotes the transcriptional activity of MYOD1 through its CDK9-mediated phosphorylation (By similarity). Interacts with CSRP3 (PubMed:9234731). Interacts with NUPR1 (By similarity). Phosphorylated by CDK9. This phosphorylation promotes its function in muscle differentiation (By similarity). Acetylated by a complex containing EP300 and PCAF. The acetylation is essential to activate target genes. Conversely, its deacetylation by SIRT1 inhibits its function (By similarity). Ubiquitinated on the N-terminus; which is required for proteasomal degradation. Methylation at Lys-104 by EHMT2/G9a inhibits myogenic activity.