Intracellular mono-ADP-ribosyltransferase that may play a role in different processes through the mono-ADP-ribosylation of proteins involved in those processes. May play a role in the unfolded protein response (UPR), by ADP-ribosylating and activating EIF2AK3 and ERN1, two important UPR effectors. May also mediate mono-ADP-ribosylation of karyopherin KPNB1 a nuclear import factor. May not modify proteins on arginine or cysteine residues compared to other mono-ADP-ribosyltransferases. L-aspartyl-[protein] + NAD(+) = 4-O-(ADP-D-ribosyl)-L-aspartyl-[protein] + nicotinamide L-lysyl-[protein] + NAD(+) = H(+) + N(6)-(ADP-D-ribosyl)-L-lysyl-[protein] + nicotinamide L-glutamyl-[protein] + NAD(+) = 5-O-(ADP-D-ribosyl)-L-glutamyl-[protein] + nicotinamide Interacts with KPNB1. The N-terminal PARP alpha-helical domain is regulatory, it packs against the catalytic domain, and may relay effector-binding event to the NAD-binding site. Auto-mono-ADP-ribosylated. Belongs to the ARTD/PARP family.