The protocadherin alpha gene cluster is one of three related clusters tandemly linked on chromosome five. The clusters have a genomic organization similar to that of B-cell and T-cell receptor gene clusters. The alpha gene cluster is composed of 15 genes and 1 pseudogene, which are members of the cadherin superfamily and related to the mouse CNR genes. The sequence of the 13 upstream genes and the pseudogene are highly similar to one another, while a subfamily (C) contains two more distantly related coding sequences. The alpha cluster genes are organized in a tandem array of 15 large, variable region exons followed by a constant region, which contains 3 exons shared by all genes in the cluster. Each variable region exon encodes an extracellular domain comprised of 6 cadherin ectodomains and a transmembrane region. The constant region exons encode a common cytoplasmic tail.