Tankyrases are members of the poly(ADP-ribose) polymerase (Parp) family that regulate telomere length in telomerase-positive human cells. There are two related homologues, tankyrase-1 and tankyrase-2. Tankyrase-1 is a protein of 1,327 amino acids and 142 kDa. The gene maps to 8p22–p23. Tankyrase-2 is a protein of 1,166 amino acids and 127 kDa. The gene maps to 10q23. Tankyrase-1 is relatively abundant in reproductive tissues (i.e., testis and ovary), whereas tankyrase-2 exhibits rather ubiquitous expression.
Tankyrase-1 has four characteristic domains: HPS, ANK, SAM, and PARP. The N-terminal HPS domain is a homopolymeric run of histidine, proline, and serine residues, the functional significance of which is unknown. The ANK domain is composed of a long stretch of 24 ANK repeats, providing a platform for protein-protein interactions. Distinct from those of ankyrins, tankyrase-1’s...