Structural phosphoproteins associated with purified measles virions and cytoplasmic nucleocapsids.

Measles virions and cytoplasmic nucleocapsids were labeled with [3H]-amino acids and [32P]-orthophosphate and were purified from infected Vero cells. When analyzed by PAGE, the two capsid-associated polypeptides (VP2 -- 69,000 daltons, VP3 -- 60,000 daltons) were shown to be phosphorylated. Characterization of the phosphorylated polypeptides by acid hydrolysis and high-voltage paper electrophoresis showed that serine was the major phosphorylated amino acid, although lesser amounts of phosphothreonine were also present. The possible role of phosphorylation in the replication cycle of the virus is discussed.