The function of PARP4 (poly(ADP-ribose) polymerase family member 4, ENSG00000102699) is as follows. Mono-ADP-ribosyltransferase that mediates mono-ADP- ribosylation of target proteins (PubMed:25043379). Component of the vault particle, which is a massive ribonucleoprotein complex that may play a role in cargo transport and signal transduction (PubMed:40691181). {ECO:0000269|PubMed:25043379, ECO:0000269|PubMed:40691181}.