Tubulointerstitial nephritis antigen (TIN-ag) is an extracellular matrix basement protein which was originally identified as a target antigen involved in anti-tubular basement membrane (TBM) antibody-mediated interstitial nephritis (TIN). Further investigations elucidated that TIN-ag plays a role in renal tubulogenesis and that TIN-ag is defected in hereditary tubulointerstitial disorder such as juvenile nephronophthisis. We previously isolated and characterized 54 kDa glycoprotein as TIN-ag. cDNA encoding rabbit and mouse TIN-ag has recently been identified. In the present study, the cDNA of the human homologue of TIN-ag was cloned and its nucleotide sequence was determined (Accession No. AB022277; the DDBJ nucleotide sequence database). Deduced amino acid sequence (476 aa) exhibited the presence of a signal peptide (1-18 aa), cysteine residues termed follistatin module, six potential glycosylation sites, and an ATP/GTP-binding site. Homology search revealed similar to 85% homology with both rabbit and mouse TIN-ag, and also some (similar to 46%) similarity with C. elegans. Human TIN-ag contained a sequence similar to several classes of extracellular matrix molecules in amino terminal region and to cathepsin family of cysteine proteinases in the carboxyl terminal region. Northern blot analysis revealed exclusive expression of this molecule in human adult and fetal kidney tissues. Using a monoclonal antibody recognizing human TIN-ag, protein expression (similar to 50 kDa) was identified in cultured COS-1 cells transfected with human TIN-ag cDNA. The human TIN-ag was mapped to chromosome 6p11.2-12 by fluorescence in situ hybridization. These results may provide further evidence for understanding TIN-ag molecule and clues for gene analysis of juvenile nephronophthisis.