WGR domain of poly(ADP-ribose) polymerase 3 and similar proteins
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-3 and similar proteins, including Arabidopsis thaliana PARP-2. PARP-3 displays a tissue-specific expression, with highest amounts found in the nuclei of epithelial cells of prostate ducts, salivary glands, liver, pancreas, and in the neurons of terminal ganglia. Unlike PARP-1 and PARP-2, PARP-3 activity is not induced by DNA strand breaks. However, it co-localizes with Polycomb group bodies and is part of complexes making up DNA-PKcs, DNA ligases III and IV, Ku70, and Ku80. PARP-3 is a nuclear protein that may be involved in transcriptional control and responses to DNA damage.