Smooth muscle cells (SM) and cardiac muscle cells-specific transcriptional factor which uses the canonical single or multiple CArG boxes DNA sequence. Acts as a cofactor of serum response factor (SRF) with the potential to modulate SRF-target genes. Plays a crucial role in cardiogenesis, urinary bladder development, and differentiation of the smooth muscle cell lineage (myogenesis) (By similarity). Homodimer. Interacts with SRF, its association does not depend on specific DNA sequences for ternary complex formation (By similarity). Interacts with MLLT7/FOXO4. Interacts (via C-terminal) with EP300 (via the CREB-binding domain). Interacts with HDAC4 and HDAC5 (By similarity). Interacts with MEF2C (By similarity). Expressed in heart, aorta, and in smooth muscle cell-containing tissues: stomach, bladder, small intestine, colon, lung, placenta and uterus. Very faint expression in prostate and skeletal muscle. Up-regulated during heart failure. The C-terminal region contains a general transcription activation domain. The N-terminal region, comprising a basic and a Gln-rich domain, confers transcriptional potency and specificity by mediating association with the MADS box of SRF. The basic domain may be required for nuclear localization. The SAP domain is important for transactivation and ternary complex formation (By similarity). Phosphorylation regulates negatively the intrinsic myocardin transcriptional activity. The disease may be caused by variants affecting the gene represented in this entry.