The presence and primary structure of a novel subunit of the mouse glutamate receptor channel, designated as gamma-2, have been revealed by cloning and sequencing the CDNA. The gamma-2 subunit has structural characteristics common to the neurotransmitter-gated ion channel family and shares a high amino acid sequence identity with the rat KA-1 subunit, thus constituting the gamma-subfamily of the glutamate receptor channel. Expression of the gamma-2 subunit together with the beta-2 subunit in Xenopus oocytes yields functional glutamate receptor channels selective for kainate.