PARP4 [poly(ADP-ribose) polymerase family, member 4] catalyzes the formation of ADP-ribose polymers covalently attached to proteins using NAD+ as a substrate. There are 6 mammalian PARP enzymes: PARP1, PARP2, PARP3, PARP4/vPARP, PARP5/Tankyrase-1, and PARP6/Tankyrase-2. PARP4 is also known as vault PARP (vPARP) due to its association with the vault particle, a 13MDa cytoplasmic ribonucleoprotein complex whose barrel-shaped structure resembles arched cathedral ceilings. vPARP has also been identified separate from the vault particle. It has been localized to the nuclear pore, mitotic spindle, and cytoplasm. It also has been shown to associate with telomerase activity. Studies of vPARP knockout mice show an increased susceptibility to carcinogen-induced tumorigenesis.