A fusion protein of the toxic and antitoxin components of a hybrid type II/IV toxin-antitoxin (TA) system. The N-terminal domain ADP-ribosylates ssDNA on a thymidine residue, while the C-terminal domain removes the modification, neutralizing the toxic effect. a thymidine in DNA + NAD(+) = an N-(ADP-alpha-D-ribosyl)-thymidine in DNA + H(+) + nicotinamide an N-(ADP-alpha-D-ribosyl)-thymidine in DNA + H2O = a thymidine in DNA + ADP-D-ribose The NAD(+)-binding element stabilizes the ADP-ribosylating turn-turn (ARTT) loop which confers substrate specificity; both domains contribute to ssDNA-binding. In the N-terminal section; belongs to the DarT ADP-ribosyltransferase family. In the C-terminal section; belongs to the DarG ADP-ribosyl glycohydrolase family. This is a fusion of 2 opposing activites; its in vivo function is unclear.