IQCJ (IQ domain-containing protein J) is a 159 amino acid protein that contains one IQ domain. Existing as four alternatively spliced isoforms, the gene encoding IQCJ maps to human chromosome 3q25.32. Chromosome 3 houses over 1,100 genes, including a chemokine receptor (CKR) gene cluster and a variety of human cancer-related gene loci. Key tumor suppressing genes on chromosome 3 include those that encode the apoptosis mediator RASSF1, the cell migration regulator HYAL1 and the angiogenesis suppressor SEMA3B.