This protein is the human homolog of mastermind, a Drosophila protein that plays a role in the Notch signaling pathway involved in cell-fate determination. There is in vitro evidence that the human homolog forms a complex with the intracellular portion of human Notch receptors and can increase expression of a Notch-induced gene. This evidence supports its proposed function as a transcriptional co-activator in the Notch signaling pathway.