Intracellular mono-ADP-ribosyltransferase that plays a role in different processes， such as protein translation and unfolded protein response (UPR)， through the mono-ADP-ribosylation of proteins involved in those processes (PubMed:22701565， PubMed:23103912， PubMed:25043379， PubMed:34314702).Acts as an inhibitor of protein translation by catalyzing mono-ADP-ribosylation of ribosomal subunits， such as RPL14 and RPS6， thereby inhibiting polysome assembly and mRNA loading (PubMed:34314702).Mono-ADP-ribosylation of ribosomal subunits is promoted by NMNAT2 (PubMed:34314702).Involved in the unfolded protein response (UPR) by ADP-ribosylating and activating EIF2AK3 and ERN1， two important UPR effectors (PubMed:23103912).May also mediate mono-ADP-ribosylation of karyopherin KPNB1 a nuclear import factor (PubMed:22701565).May not modify proteins on arginine or cysteine residues compared to other mono-ADP-ribosyltransferases (PubMed:22701565).