The 193-kD vault protein, VPARP, is a novel Poly(ADP-ribose) polymerase

Mammalian vaults are ribonucleoprotein (RNP) complexes, composed of a small ribonucleic acid and three proteins of 100, 193, and 240 kD in size. The 1 00-kD major vault protein (MVP) accounts for >70% of the particle mass. We have identified the 193-kD vault protein by its interaction with the MVP in a yeast two-hybrid screen and confirmed its identity by peptide sequence a nalysis. Analysis of the protein sequence revealed a region of similar to 3 50 amino acids that shares 28% identity with the catalytic domain of poly(A DP-ribose) polymerase (PARP), PARP is a nuclear protein that catalyzes the formation of ADP-ribose polymers in response to DNA damage, The catalytic d omain of p193 was expressed and purified from bacterial extracts. Like PARP , this domain is capable of catalyzing a poly(ADP-ribosyl)ation reaction; t hus, the 193-kD protein is a new PARP. Purified vaults also contain the pol y(ADP-ribosyl)ation activity, indicating that the assembled particle retain s enzymatic activity. Furthermore, we show that one substrate for this vaul t-associated PARP activity is the MVP. Immunofluorescence and biochemical d ata reveal that p193 protein is not entirely associated with the vault part icle, suggesting that it map interact with other protein(s). A portion of p 193 is nuclear and localizes to the mitotic spindle.