A trimeric cell-cell fusion complex that serves as a scaffold for zippering up the extracellular domains, bringing the transmembrane segments into close proximity such that they can continue zippering within the two membranes into one. Two prefusion monomers cluster at the surface of adjacent cells. Parallel EFF-1 interactions occur across cells and a third monomer, which can come from either cell, adds on to make an intermediate, extended trimer.
EFF-1 complex