Toxic component of a type II toxin-antitoxin (TA) system. Expression in E.coli inhibits cell growth; bacteriostasis is neutralized by expression of cognate antitoxin ParS. ADP-ribosylates E.coli ribose-phosphate pyrophosphokinase (RPPK, prs) using NAD(+) in vitro; ADP-ribosylates RPPK on 'Lys-182' and 'Ser-202'. Cannot use NADP(+). Also auto-ADP-ribosylates in vitro; in the presence of RPPK auto-ADP-ribosylation decreases. Homodimer, forms heterotetrameric ParS(2)-ParT(2) complexes. Forms salt bridges between the 2 toxin molecules mediated by Glu-127 Glu-128 on one subunit and Arg-46 Arg-149 on the other. Consumes NAD(+) and auto-ADP-ribosylates on the tryptic fragment Ala-47-Arg-66 in vitro. Also auto-ADP-ribosylates using NADP(+). Belongs to the MbcT/ParT/Res family.