Genes encoding three new members of the leukocyte antigen 6 superfamily and a novel member of Ig superfamily, together with genes encoding the regulatory nuclear chloride ion channel protein (hRNCC) and a N-omega-N-omega-dimethylarginine dimethylaminohydrolase homologue, are found in a 30-kb segment of the MHC class III region

Many of the genes in the class III region of the human MHC encode proteins involved in the immune and inflammatory responses. We have sequenced a 30-k b segment of the MHC class III region lying between the heat shock protein 70 and TNF genes as part of a program aimed at identifying genes that could be involved in autoimmune disease susceptibility. The sequence analysis ha s revealed the localization of seven genes, whose precise position and orde r is cen-G7-G6-G6A-G6B-G6C-G6D-G6E-tel, five of which are fully encoded in the sequence, allowing their genomic structures to be defined. Three of the m (G6C, G6D, and G6E) encode putative; proteins that belong to the Ly-6 sup erfamily, known to be GPI-anchored proteins attached to the cell surface. M embers of the family are specifically expressed and are important in leukoc yte maturation. A fourth gene, G6B, encodes a novel member of the Ig superf amily containing a single Ig V-like domain and a cytoplasmic tail with seve ral signal transduction features. The G6 gene encodes a regulatory nuclear chloride ion channel protein, while the G6A gene encodes a putative homolog ue of the enzyme N-omega,N omega-dimethylarginine dimethylaminohydrolase wh ich is thought to be involved in regulating nitric oxide synthesis. In addi tion, three microsatellite markers, 9N-1, 82-2, and D6S273 are contained wi thin the sequence, the last two of which have been reported to be strongly associated with the autoimmune disease ankylosing spondylitis.