Nodal Modulator (NOMO, also known as pM5) is a 130 kDa type I membrane protein with no recognizable functional motif. NOMO is a binding partner of Nicalin, a nicastin-related protein. The Nicalin/NOMO complex is localized in the endoplasmic reticulum and functions as an antagonist for Nodal and Activin signaling. Three copies of the NOMO gene, encoding NOMO isoforms 1, 2 and 3 have been described. The extracellular domains (ECD) of the isoforms share 99% amino acid sequence homology. The ECD of human NOMO and mouse NOMO share 94% amino acid sequence homology.