Liver-expressed chemokine (LEC) is a CC chemokine that is selectively expressed in the liver. We report here the structures of the human and mouse genes for LEC. The human LEC gene (SCYA16) was isolated from a bacterial artificial chromosome (BAC) clone that also contained CC chemokine genes for MPIF-1/Ckbeta8, HCC-2/Lkn-1/MIP-5/MIP-1delta, and HCC-1. The LEC gene is approximately 5.0 kb in length and has a three-exon and two-intron structure common to most CC chemokine genes. However, the promoter region is devoid of a typical TATA box, and transcription initiates at multiple sites. The gene for CC chemokine HCC-1, which is most similar to LEC, is located approximately 2.2 kb upstream from the 5' end of the LEC gene in a head-to-tail fashion. The mouse DNA fragment that hybridized with the human LEC cDNA was isolated from a BAC clone that also contained the CC chemokine genes for C10, MRP-2/CCF18/MIP-1gamma, and RANTES. Sequence analysis revealed that the isolated gene does not encode a functional chemokine because of deletions, insertions, and base changes. Southern blot analysis revealed that the sequence isolated from the BAC clone was the only one hybridizing with human LEC cDNA in the mouse genome. Therefore, mice may have only an LEC pseudogene.