A gene, GS2 (DXS1283E), was isolated from a CpG island located approximately midway between the steroid sulfatase (STS) and the Kallmann syndrome (KAL1) loci on the distal short arm of the human X chromosome. DNA sequencing of a GS2 cDNA clone revealed an open reading frame for a basic protein of 253 amino acid residues. A polymorphic CT dinucleotide repeat was found in the 3' untranslated region. The GS2 gene is expressed in all human tissues examined, including heart, brain, placenta, lung, liver, muscle, kidney, pancreas, and spleen. Several GS2 transcripts, ranging in size from 1.1 to 5.8 kb, were found among different tissues, suggesting tissue-specific processing of the GS2 transcript. Characterization of GS2 genomic clones revealed that the gene consists of 7 exons spanning over 26 kb, with a CpG island located in the first intron. The GS2 gene is transcribed toward Xpter, in the same direction as KAL1 but opposite to that of STS.