The human gene encoding a novel tubulointerstitial nephritis antigen (TIN-ag)-related protein (TIN-ag-RP) was isolated, and its genomic organization was determined BLAST searches revealed the highest degree of homology to several mammalian TIN-ag orthologues, and a weak homology to cathepsin B-like proteases. The 12 kb gene was mapped by fluorescence In situ hybridization to chromosome 1p34.2-3, a locus neither related to that of the human TIN-ag (6p11.2-12) nor to that of cathepsin B (8p22-23.1). The TIN-ag-RP is encoded in ten exons with introns ranging from 83 bp to 4 kb. in addition, the gene contained one exon in the 5'UTR, but none in the 3'UTR. Five of the 10 splice sites of the TIN-ag-RP gene were fully conserved when compared to a related gene of C. elegans, whereas only one splice site was identical to those found in cathepsin B genes. Furthermore, human TIN-ag-RP tagged with the T7-epitope, was expressed in HeLa cells, and was found to be localized in vesicular compartments as well as secreted into the medium suggesting the involvement of the endosomal trafficking pathway. Eased on the high degree of homology of the amino acid sequences and genomic organization between TIN-ag-RP and TIN-ag, we suggest that both molecules may form a distinct group or family of TEN-ag-like proteins.