The sequences making up this family are annotated as, or are similar to, Ly49 receptors. These are type II transmembrane receptors expressed by mouse natural killer (NK) cells. They are classified as being activating (e.g.Ly49D and H) or inhibitory (e.g. Ly49A and G), depending on their effect on NK cell function. They are members of the C-type lectin receptor superfamily, and in fact in many family members this region is found immediately N-terminal to a lectin C-type domain (pfam00059).