Mono-ADP-ribosyltransferase that mediates mono-ADP-ribosylation of target proteins. L-aspartyl-[protein] + NAD(+) = 4-O-(ADP-D-ribosyl)-L-aspartyl-[protein] + nicotinamide L-glutamyl-[protein] + NAD(+) = 5-O-(ADP-D-ribosyl)-L-glutamyl-[protein] + nicotinamide Component of the vault ribonucleoprotein particle, at least composed of MVP, PARP4 and one or more vault RNAs (vRNAs) (PubMed:10477748). Interacts with TEP1 (PubMed:10551828, PubMed:15169895). Also found in the nucleus, associated with mitotic spindles. Widely expressed; the highest levels are in the kidney; also detected in heart, placenta, lung, liver, skeletal muscle, spleen, leukocytes and pancreas. Belongs to the ARTD/PARP family. Was initially thought to mediate to mediate poly-ADP-ribosylation of proteins (PubMed:10477748). However, it was later shown to act as a mono-ADP-ribosyltransferase (PubMed:25043379). Extended N-terminus.