ADP-ribosyltransferase which, in association with E3 ligase DTX3L, plays a role in DNA damage repair and in immune responses including interferon-mediated antiviral defenses (PubMed:16809771, PubMed:23230272, PubMed:26479788, PubMed:27796300). Within the complex, enhances DTX3L E3 ligase activity which is further enhanced by PARP9 binding to poly(ADP-ribose) (PubMed:28525742). In association with DTX3L and in presence of E1 and E2 enzymes, mediates NAD(+)-dependent mono-ADP-ribosylation of ubiquitin which prevents ubiquitin conjugation to substrates such as histones (PubMed:28525742). During DNA repair, PARP1 recruits PARP9/BAL1-DTX3L complex to DNA damage sites via PARP9 binding to ribosylated PARP1 (PubMed:23230272). Subsequent PARP1-dependent PARP9/BAL1-DTX3L-mediated ubiquitination promotes the rapid and specific recruitment of 53BP1/TP53BP1, UIMC1/RAP80, and BRCA1 to DNA damage sites (PubMed:23230272, PubMed:28525742). In response to DNA damage, PARP9-DTX3L complex is required for efficient non-homologous end joining (NHEJ); the complex function is negatively modulated by PARP9 activity (PubMed:28525742). Dispensable for B-cell receptor (BCR) assembly through V(D)J recombination and class switch recombination (CSR) (By similarity). In macrophages, positively regulates pro-inflammatory cytokines production in response to IFNG stimulation by suppressing PARP14-mediated STAT1 ADP-ribosylation and thus promoting STAT1 phosphorylation (PubMed:27796300). Also suppresses PARP14-mediated STAT6 ADP-ribosylation (PubMed:27796300). [protein]-C-terminal glycine + NAD(+) = [protein]-C-terminal O-(ADP-D-ribosyl)-glycine + nicotinamide Binding to poly(ADP-ribose) does not affect its activity. Forms a stable complex with E3 ligase DTX3L; the interaction is required for PARP9 mediated ADP-ribosylation of ubiquitin (PubMed:12670957, PubMed:28525742). Interacts (via PARP catalytic domain) with DTX3L (via N-terminus) (PubMed:26479788). Forms a complex with STAT1 and DTX3L independently of IFNB1 or IFNG-mediated STAT1 'Tyr-701' phosphorylation (PubMed:26479788). Forms a complex with STAT1, DTX3L and histone H2B H2BC9/H2BJ; the interaction is likely to induce H2BC9/H2BJ ubiquitination (PubMed:26479788). Interacts (via N-terminus) with STAT1 (PubMed:26479788). Interacts with PARP14 in IFNG-stimulated macrophages; the interaction prevents PARP14-mediated STAT1 and STAT6 ADP-riboslylation (PubMed:27796300). Interacts with PARP1 (when poly-ADP-ribosylated) (PubMed:23230272). Shuttles between the nucleus and the cytosol (PubMed:16809771). Translocates to the nucleus in response to IFNG or IFNB1 stimulation (PubMed:26479788). Export to the cytosol depends on the interaction with DTX3L (PubMed:16809771). Localizes at sites of DNA damage in a PARP1-dependent manner (PubMed:23230272, PubMed:28525742). Expressed in lymphocyte-rich tissues, spleen, lymph nodes, peripheral blood lymphocytes and colonic mucosa (PubMed:11110709, PubMed:16809771). Expressed in macrophages (PubMed:27796300). Also expressed in nonhematopoietic tissues such as heart and skeletal muscle (PubMed:11110709, PubMed:16809771). Isoform 2 is the predominant form (PubMed:11110709). Most abundantly expressed in lymphomas with a brisk host inflammatory response (PubMed:11110709, PubMed:16809771). In diffuse large B-cell lymphomas tumors, expressed specifically by malignant B-cells (PubMed:11110709, PubMed:16809771). Up-regulated by IFNG in macrophages and in B-cell lymphoma cell lines (PubMed:16809771, PubMed:27796300, PubMed:26479788). Up-regulated by IFNB1 or viral infection (PubMed:26479788). Down-regulated by IL4 in macrophages (PubMed:27796300). Macro domains 1 and 2 may be involved in the binding to poly(ADP-ribose) (PubMed:28525742, PubMed:26479788). Macro domain 2 is required for recruitment to DNA damage sites (PubMed:23230272). Macro domains 1 and 2 are probably dispensable for the interaction with STAT1 and DTX3L and for STAT1 phosphorylation (PubMed:26479788). ADP-ribosylated by PARP14. Overexpressed at significantly higher levels in fatal high-risk diffuse large B-cell lymphomas (DLB-CL) compared to cured low-risk tumors. Overexpression in B-cell lymphoma transfectants may promote malignant B-cell migration. May therefore be involved in promoting B-cell migration and dissemination of high-risk DLB-CL tumors (PubMed:11110709). Belongs to the ARTD/PARP family.