Human Translin is a novel DNA end binding protein that specifically recognizes consensus sequences at the breakpoint junctions in chromosomal translocations, mostly involving immunoglobulin (Ig)/T-cell receptor gene segments, in human lymphoid neoplasms. We have recently cloned a full-length human Translin cDNA using peptide sequence information obtained from the purified protein. From comparisons of the amino acid sequences in humans and other vertebrates, we conclude that Translin has been highly conserved during evolution, especially at the leucine zipper motif and the basic region, which is thought to be the DNA binding domain. Analysis of the human and mouse Translin genes revealed that they have identical genomic structures consisting of six exons, five introns, and a GC-rich upstream region. In situ hybridization and physical mapping of somatic cell hybrids allowed localization of the gene to human chromosome 2q21.1.