Cadherins are calcium-dependent cell-cell adhesion molecules, and protocadherins constitute a subfamily of nonclassic cadherins. The PCDHB gene cluster encodes a family of protocadherins. Unlike the PCDHA and PCDHG gene clusters, in which mRNAs are produced by splicing a single upstream variable exon to 3 downstream constant region exons, PCDHB mRNAs are encoded by single-exon genes. Thus, each PCDHB gene encodes the extracellular, transmembrane, and short cytoplasmic domains of the protein. In contrast to the PCDHA and PCDHG clusters, the PCDHB gene cluster does not have a downstream constant region. The C-terminal cytoplasmic domains of PCDHB proteins are therefore encoded by the single-exon PCDHB genes.