A fifth member of the polycystin family, polycystin-L2, is encoded by PKD2L2 in the human and Pkd2l2 in the mouse. Pkd2l2 is a novel member of the polycystic kidney disease (PKD) gene family in mammals and located on chromosome band 5q31. Prominently expressed in testis. Full-length cDNA sequences for both mouse and human polycystin-L2 were obtained from testis cDNA. Sequence analysis predicts that the mouse and human polycystin-L2 proteins consist of 621 and 624 amino acid residues, respectively. Polycystin-L2 has significant homology with polycystins-L and -2, with similarities of 58 and 59%, respectively. Both human and murine polycystin-L2 proteins are predicted to have seven putative transmembrane (TM) domains, and, by comparison with transient receptor potential channels, the six carboxyl-terminal TM domains are likely to constitute an ion channel subunit.