The complete sequence of the polycystic kidney disease gene (PKD1) and its transcript have been described. The predicted protein is not a member of a previously described gene family, but contains several structural motifs that are present in proteins of known function. Most of these domains are present in the extracellular parts of proteins involved in interactions with other proteins and carbohydrates. The PKD1 gene product also contains potential transmembrane sequences. The molecule is likely to be involved in cell-cell or cell-matrix interactions, which is consistent with the different manifestations of polycystic kidney disease.