BOTH ALLELIC FORMS OF THE RAT T-CELL DIFFERENTIATION MARKER RT6 DISPLAY NICOTINAMIDE ADENINE-DINUCLEOTIDE (NAD)-GLYCOHYDROLASE ACTIVITY, YET ONLY RT6.2 IS CAPABLE OF AUTOMODIFICATION UPON INCUBATION WITH NAD

The finding that recently cloned mono-ADP-ribosyltransferases show seq uence similarity to the rat T cell differentiation marker RT6 has led us to investigate the enzymatic activity of this alloantigenic system. To search for ADP-ribosylation of cell surface proteins,T cell popula tions from RT6.1- and RT6.2-expressing rat strains, as well as RT6.1() and RT6.2(+) T-T hybridoma cell lines, were incubated with [P-32]nic otinamide adenine dinucleotide (NAD). All RT6.2(+), but no RT6.1(+) or RT6(-) cells, show incorporation of radioactivity into a single prote in which could be identified as RT6.2 by immunoprecipitation with mono clonal antibodies. This automodification of RT6.2 is covalent, require s intact NAD as substrate, and displays characteristics typical for li nkage of ADP-ribose to arginine. The alloantigens RT6.1 and RT6.2 diff er in ten amino acids, RT6.2 having two arginine residues not present in RT6.1. Both alloantigens were found to display potent NAD-glycohydr olase activity.