We have cloned a cDNA that codes for mouse liver-specific transporter-1, mouse lst-1. The cDNA is comprised of 3296 base pairs and it contains a coding sequence for a protein of 689 amino acids with 12 putative transmembrane domains. The deduced amino acid sequence of the mouse lst-1 shares 64 and 77% identities with the reported human and rat lsts, respectively, Northern blot analysis demonstrates that mouse lst-1 mRNA is expressed exclusively in liver, We also report here the structural organization of the mouse lst-1 gene as the first evidence for the structure of a gene encoding an Ist. The mouse lst-1 gene spans approximately 60 kbp in length and consists of 16 exons, including two noncoding exons, All the introns are flanked by GT-AG consensus splice sequences. 5'-Rapid Amplification of cDNA Ends (RACE) analyses demonstrate three splice variant mRNAs involving the noncoding exon 2 and exon 3, The 5'-flanking region of the gene contains consensus CAAT and TATA boxes and several potential binding sites for transcription factors for CAAT enhancer binding protein (C/EBP) and hepatocyte nuclear factors (HNF-3 beta, HFH-1, and HFH-2), transcription factors important for liver-specific gene expression.