SUMMARYWe report the identification and characterization of a clone for the DNA binding proteinSON, which we have isolated from a human keratinocyte cDNA library. Using this clone we have found that theSONgene is expressed in different cell types and that homologous sequences can be detected in vertebrate and insect genomic DNA. Using the polymerase chain reaction (PCR) to amplifySONsequences from a panel of somatic cell hybrids we have assigned the gene encoding humanSONto chromosome 21. By use of hybrids containing regions of chromosome 21 the localization has been refined to 21q 22. 1‐q22.