This domain family is found in eukaryotes, and is approximately 190 amino acids in length. This domain is the penultimate C terminal domain from the protein ste5 which co-catalyzes the phosphorylation of fus3 by ste7. It is involved in the MAPK pathways. This domain is the minimal scaffold domain of ste5. It binds to the mitogen activated protein kinase fus3 before it is phosphorylated.