Major vault protein of electric ray is a phosphoprotein

The major vault protein is the predominant member of a large cytosolic ribonucleoprotein particle, named vaults. Vaults are abundant in nerve terminals of the electric organ of Torpedo marmorata. Negative staining of isolated vaults reveals particle dimensions of 45x65 nm in size. Comparison of the major vault protein (MVP100) from the two electric ray species Torpedo marmorata and Discopyge ommata reveals few microheterogeneities in amino acid sequence. Potential phosphorylation sites for various protein kinases are highly conserved. Phosphorylation studies demonstrate that the major vault protein of Torpedo is a substrate of various protein kinases. MVP100 is phosphorylated by protein tyrosine kinase in vivo and protein kinase C and casein kinase II in vitro. Inhibitors and activators of protein kinases specifically modulate the phosphorylation of MVP100.