ADP-ribosyltransferase 4 (Dombrock blood group), also known as Mono-ADP-ribosyltransferase 4(ART4), Dombrock blood group carrier molecule and CD297, is a protein that contains a mono-ADP-ribosylation (ART) motif. It is a member of the ADP-ribosyltransferase gene family but enzymatic activity has not been demonstrated experimentally. ADP-ribosyltransferase catalyzes the ADP-ribosylation of arginine residues in proteins. Mono-ADP-ribosylation is a posttranslational modification of proteins that is interfered with by a variety of bacterial toxins including cholera, pertussis, and heat-labile enterotoxins of E. coli. ART4 could be detected on HEL cells and erythrocytes by FACS analysis while it was absent from activated monocytes, despite the presence of ART4 mRNA in these cells. ART is also known as the carrier of the Dombrock blood group alloantigens (Do) which is glycosylphosphatidylinosotol-anchored to the erythrocyte membrane.