The function of ENSG00000138617 (PARP16, poly(ADP-ribose) polymerase family member 16) is as follows. 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). {ECO:0000269|PubMed:22701565, ECO:0000269|PubMed:23103912, ECO:0000269|PubMed:25043379, ECO:0000269|PubMed:34314702}.