serum response factor is a member of the mads (mcm1, agamous, deficiens, and srf) box superfamily of transcription factors. this protein binds to the serum response element (sre) in the promoter region of target genes. this protein regulates the activity of many immediate early genes, for example c-fos, and thereby participates in cell cycle regulation, apoptosis, cell growth, and cell differentiation. this gene is the downstream target of many pathways; for example, the mitogen-activated protein kinase pathway (mapk) that acts through the ternary complex factors (tcfs).