The WGR domain is found in a variety of eukaryotic poly(ADP-ribose) polymerases (PARPs). It has been called WGR after the most conserved central motif of the domain. The domain typically occurs together with a catalytic PARP domain, and is between 70 and 80 residues in length. It has been proposed to function as a nucleic acid binding domain. PARPs catalyze the NAD(+)-dependent synthesis of ADP-ribose polymers and their addition to various nuclear proteins. Higher eukaryotes contain several PARPs and and there may be up to 17 human PARP-like proteins, with three of them (PARP-1, PARP-2, and PARP-3) containing a WGR domain. The synthesis of poly-ADP-ribose requires multiple enzymatic activities for initiation, trans-ADP-ribosylation, elongation, branching, and release of the polymer from the enzyme. This subfamily is composed of human PARP-2 and similar proteins. Similar to PARP-1, PARP-2 is ubiquitously expressed and its activity is induced by DNA strand breaks. It also plays a role in cell differentiation, cell death, and maintaining genomic stability. Studies on mice deficient with PARP-2 shows that it is important in fat storage, T cell maturation, and spermatogenesis.